Cytoplasmic Mislocalization Of P27 Research Articles

LOX upregulates FAK phosphorylation to promote metastasis in osteosarcoma

Osteosarcoma is a malignant bone tumor that commonly occurs in the pediatric population. Despite the use of chemotherapy and surgery, metastasis remains to be the leading cause of death in patients with osteosarcoma. We have previously reported that cytoplasmic mislocalization of p27 is associated with a poor outcome in osteosarcoma. In this study, we further show that lysyl oxidase (LOX) expression was associated with p27 mislocalization. LOX is an enigmatic molecule that acts as a tumor suppressor or a metastatic promoter; however, its role in osteosarcoma is still unclear. Hence, we performed both in vitro and in vivo analyses to dissect the role of LOX in osteosarcoma. The result of our survival analysis indicated that LOX expression significantly correlated with a poor outcome in osteosarcoma with or without controlling for the initial metastasis status (P < 0.05). Functionally, we found that higher LOX expression promoted osteosarcoma cell proliferation, migration, and invasiveness in vitro and produced a higher number of mice with pulmonary metastases in an orthotopic xenograft mouse model. Mechanistically, phospho-FAK was increased in osteosarcoma cells with high LOX expression. Our results further showed that FAK inhibition significantly reduced tumor cell proliferation and migration in vitro as well as LOX-mediated metastasis in mice. Together, our findings suggest that there is a novel link between p27 mislocalization and LOX expression. LOX plays a pivotal role in osteosarcoma metastasis by upregulating FAK phosphorylation. FAK inhibition may constitute a promising therapeutic strategy to reduce the development of metastasis in osteosarcoma with LOX overexpression.

Abstract 2445: Cytoplasmic mislocalization of p27 promotes metastasis and its autoantibody correlates with prognosis in osteosarcoma

Abstract Development of metastasis is the major cause of death in osteosarcoma, which is the most common malignant bone tumor in children and young adults. However, detection of metastasis relies solely on imaging techniques and targeted treatments of metastatic patients are still not available to improve the dismal outcome. Using an immunoproteomic approach, we identified that p27 autoantibody was significantly elevated in the plasma of high-risk osteosarcoma patients. Results of immunohistochemistry showed that cytoplasmic mislocalization of p27 occurred in a majority of osteosarcoma cases and in highly metastatic osteosarcoma cell lines. We demonstrated that ectopic expression of cytoplasmic p27 and shRNA-mediated gene silencing promoted and inhibited, respectively, the migration and invasion of osteosarcoma cells. Additionally, a mutation in S10 or T198, but not T157, phosphosite abolished the pro-migration and invasion phenotypes of cytoplasmic p27, possibly through a RhoA-related mechanism. Furthermore, mice injected with cells carrying cytoplasmic p27 increased the development of pulmonary metastasis when compared to an empty vector control. Lastly, using a large cohort of serum samples (n = 233), we showed that a higher level of the p27 autoantibody significantly correlated with poor overall and event-free survival of osteosarcoma (p &amp;lt; 0.05). Together, our results suggest that the circulating p27 autoantibody can be used as a prognostic biomarker at diagnosis and cytoplasmic mislocalization of p27 is a frequent event in osteosarcoma, which can promote tumor cell motility and invasiveness as well as metastasis formation. Targeting specific p27 phosphorylations may provide a novel therapeutic approach for osteosarcoma patients with metastasis. Citation Format: Manjula Nakka, Yiting Li, Aaron J. Kelly, Ching C. Lau, Mark Krailo, Donald A. Barkauskas, John Hicks, Tsz-Kwong Man. Cytoplasmic mislocalization of p27 promotes metastasis and its autoantibody correlates with prognosis in osteosarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2445.

Loss of p27 Associated with Risk for Endometrial Carcinoma Arising in the Setting of Obesity.

Endometrial carcinoma (EC) exhibits the strongest association with obesity of all cancers. Growth of these tumors is driven by PI3K/AKT activation, and opposed by tumor suppressors, including the tuberous sclerosis complex 2 (TSC-2) and p27, with inactivation of TSC2 and loss or cytoplasmic mislocalization of p27 both being linked to PI3K/AKT activation. However, little is known about the involvement of p27 in the development of EC arising in the setting of obesity, especially its role early in disease progression. Using a panel of EC cell lines, in vitro studies using PI3K inhibitors provided evidence that p27 rescue contributes to the efficacy of interventions that inhibit endometrial cell growth. In "at risk" obese patients, and in an animal model of obesity-associated EC (Tsc2-deficient Eker rats), p27 was moderately-to-severely reduced in both "normal" endometrial glands as well as in endometrial complex atypical hyperplasia (obese women), and endometrial hyperplasia (obese rats). In obese Eker rats, an energy balance intervention; caloric restriction from 2-4 months of age, reduced weight, increased adiponectin and lowered leptin to produce a favorable leptin:adiponectin ratio, and reduced circulating insulin levels. Caloric restriction also increased p27 levels, relocalized this tumor suppressor to the nucleus, and significantly decreased hyperplasia incidence. Thus, dietary and pharmacologic interventions that inhibit growth and decrease risk for development of endometrial lesions are associated with increased expression and nuclear (re)localization of p27. These data suggest that p27 levels and localization may be useful as a biomarker, and possible determinant, of risk for EC arising in the setting of obesity.

Abstract 1622: The AKT inhibitor reverses protein trafficking and inhibits tumor cell motility of p27-mislocalized osteosarcoma cells

Abstract Osteosarcoma is the most common malignant bone tumor in children. The development of metastasis remains to be the leading cause of death in osteosarcoma. This clinical challenge urges the development of a novel therapeutic strategy to improve the survival of the metastatic patients. mTOR has recently been regarded as a potential target for metastatic osteosarcoma. However, because of its feedback loop in the pathway, it has become clear that inhibition of mTOR alone would not yield effective therapeutics. More importantly, it is still not clear if the mTOR upstream kinases phosphorylate other important molecules that can also promote metastasis. Our lab has recently demonstrated that a vast majority of osteosarcoma cases harbor cytoplasmic mislocalization of p27. p27 is a tumor suppressor gene that regulates normal cell cycle progression when it is localized in the nucleus. We and others have indicated that p27 acquires a new pro-metastatic function in the cytoplasm of osteosarcoma and other tumors. To evaluate if this observation has any therapeutic significance, our lab has created a set of p27 phosphomutants and found that specific phosphorylations (S10 and T198) are important for the pro-metastatic function in the cytoplasm. Furthermore, shRNA-mediated gene silencing experiments showed that knocking down the expression of p27 decreased the motility of metastatic LM7 cells. Since AKT, the upstream kinase of mTOR, has shown to phosphorylate p27, we tested if AKT inhibitors have any effect on the migration/invasion ability of three osteosarcoma cell lines (LM7, MG63 and G292) that harbor the p27 mislocalization. The results showed that both the AKT1/2 inhibitor and the PI3K/mTOR dual inhibitor PP242, but not mTORC1 inhibitor rapamycin, reduced the tumor cell migration/invasion ability. Interestingly, the inhibitors could also reverse the protein trafficking of p27 into the nucleus. These results suggest that the inhibitors may be able to inhibit the pro-metastatic function and restore the cell cycle inhibitory function of p27. Our long-term goal is to develop a precision medicine approach that will ultimately improve the outcome of metastatic osteosarcoma. By targeting the p27 mislocalization, we believe that we will develop a novel and clinically applicable therapeutic strategy that would eradicate metastatic osteosarcoma and improve the outcome of children affected by this tumor. Citation Format: Xiang Chen, Yiting Li, Manjula Nakka, Tsz Kwong Man. The AKT inhibitor reverses protein trafficking and inhibits tumor cell motility of p27-mislocalized osteosarcoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1622. doi:10.1158/1538-7445.AM2015-1622

BCR-ABL1 promotes leukemia by converting p27 into a cytoplasmic oncoprotein

AbstractRecent studies have revealed that p27, a nuclear cyclin-dependent kinase (Cdk) inhibitor and tumor suppressor, can acquire oncogenic activities upon mislocalization to the cytoplasm. To understand how these antagonistic activities influence oncogenesis, we dissected the nuclear and cytoplasmic functions of p27 in chronic myeloid leukemia (CML), a well-characterized malignancy caused by the BCR-ABL1 tyrosine kinase. p27 is predominantly cytoplasmic in CML and nuclear in normal cells. BCR-ABL1 regulates nuclear and cytoplasmic p27 abundance by kinase-dependent and -independent mechanisms, respectively. p27 knockdown in CML cell lines with predominantly cytoplasmic p27 induces apoptosis, consistent with a leukemogenic role of cytoplasmic p27. Accordingly, a p27 mutant (p27CK−) devoid of Cdk inhibitory nuclear functions enhances leukemogenesis in a murine CML model compared with complete absence of p27. In contrast, p27 mutations that enhance its stability (p27T187A) or nuclear retention (p27S10A) attenuate leukemogenesis over wild-type p27, validating the tumor-suppressor function of nuclear p27 in CML. We conclude that BCR-ABL1 kinase-dependent and -independent mechanisms convert p27 from a nuclear tumor suppressor to a cytoplasmic oncogene. These findings suggest that cytoplasmic mislocalization of p27 despite BCR-ABL1 inhibition by tyrosine kinase inhibitors may contribute to drug resistance, and effective therapeutic strategies to stabilize nuclear p27 must also prevent cytoplasmic mislocalization.

Abstract 2224: Targeted PI3K/mTOR inhibition impairs tumor cell motility and bone metastatic outgrowth via modulation of p27

Abstract The pleiotropic oncogenic effects of PI3K/mTOR have stimulated development of catalytic PI3K and mTOR inhibitors for the treatment of cancer. Present data provide a novel rationale for the use of dual PI3K/mTOR inhibitors to oppose tumor motility, invasion and metastasis. Cytoplasmic mislocalization of p27 is implicated as a key downstream driver of PI3K/mTOR-dependent tumor cell motility in vitro and bone metastatic outgrowth in vivo. Here, we report that PI3K/mTOR-kinase inhibition with PF-04691502 impairs breast cancer metastasis to bone, in part via effects on p27. Low-dose PF-04691502 impaired motility and invasion of highly PI3K/mTOR activated, bone-metastatic MDA-MB-1833 cells in vitro without affecting apoptosis or proliferation. Moreover, drug pre-treatment impaired bone metastasis in vivo. PF-04691502 decreased cytoplasmic p27pT157 and p27pT198, and p27T157D/T198D overexpression conferred resistance to inhibition of motility by PF-04691502. p27 knockdown in MDA-MB-1833 relieved RhoA-ROCK inhibition, decreased cell motility/invasion in vitro, and bone metastasis in vivo. p27 knockdown also reversed EMT phenotypic markers in MDA-MB-1833, as did PI3K/mTOR inhibition, demonstrating that p27 may be critical for maintenance of the EMT cellular program. Indeed, loss of cytoplasmic p27 reversed expression of an EMT gene profile supporting the notion that p27 acts as a key mediator of metastasis downstream of PI3K/mTOR. Cytoplasmic p27 in human cancers may prove to be a useful predictive marker to assess both PI3K/mTOR activation and the potential efficacy of catalytic PI3K/mTOR inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2224. doi:1538-7445.AM2012-2224

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Cytoplasmic mislocalization of p27 and CDK2 mediates the anti-migratory and anti-proliferative effects of Nodal in human trophoblast cells

p27(Kip1), a cyclin-dependent kinase (CDK) inhibitor, is a multi-functional protein that regulates various cellular activities. Trophoblast proliferation, migration and invasion are some of the key processes of placental development. We have recently reported that Nodal, a member of the transforming growth factor-β (TGF-β) superfamily, inhibits human trophoblast cell proliferation, migration and invasion. In the present study, we investigated the mechanism by which Nodal regulates trophoblast activities. We found that Nodal increased p27 mRNA and protein levels by enhancing their stability. Interestingly, Nodal signaling also induced nuclear export of p27 and CDK2. Cytoplasmic translocation of p27 induced by Nodal requires p27 phosphorylation at S10. In addition, Nodal enhanced the association of p27 with CDK2, CDK5 and a microtubule-destabilizing protein, stathmin, and induced stathmin phosphorylation at S25 and S38. Furthermore, Nodal increased tubulin stability as revealed by immunofluorescent staining of acetylated tubulin. Finally, silencing of p27 reversed the inhibitory effect of Nodal on trophoblast cell proliferation, migration and invasion. Taken together, our findings revealed a novel function of simultaneous p27 and CDK2 cytoplasmic mislocalization in mediating growth-factor-regulated cell proliferation, migration and invasion.

Promotion of cytoplasmic mislocalization of p27 by Helicobacter pylori in gastric cancer

The cyclin-dependent kinase inhibitor p27 plays an important role in cell cycle regulation. Reduced expression of p27 is commonly associated with poor prognosis in many malignancies, including gastric cancer. Cytoplasmic p27 mislocalization may be an additional indicator of high-grade tumors and poor prognosis in cancer. Since chronic infection by Helicobacter pylori is the most important risk factor for gastric cancer development, we evaluated the effects of H. pylori on p27 expression and localization in gastric cancer cells. Co-culture of gastric cells with H. pylori induced cytoplasmic p27 expression and reduced nuclear p27 expression in vitro. Cytoplasmic p27 expression was associated with and dependent upon phosphorylation of p27 at T157 and T198: wild type p27 accumulated in the cytoplasm, but non-phosphorylatable mutants affecting T157 or T198 were nuclear in H. pylori infected cells. These post-translational p27 changes were secondary to activation of cellular PI3K and AKT signaling pathways and dependent upon a functional H. pylori cag pathogenicity island. We investigated the clinical significance of cytoplasmic p27 mislocalization in 164 cases of resected gastric cancer in tissue microarrays. In 97 cases (59%) cytoplasmic p27 mislocalization was observed, and this was associated with increased mortality in multivariate analysis. These results show that H. pylori infection induces AKT/PI3K-mediated phosphorylation of p27 at T157 and T198 to cause cytoplasmic p27 mislocalization in gastric cancer, and that p27 mislocalization is an adverse prognostic feature in gastric cancer. This is the first demonstration of the translocation of a specific bacterial virulence factor that post-translationally regulates a host cell cyclin-dependent kinase inhibitor. This is of particular significance because p27 has both tumor-suppressive and oncogenic activities, depending upon its subcellular localization. Cytoplasmic mislocalization of p27 induced by H. pylori may be an important mechanistic link between H. pylori infection and gastric carcinogenesis.

CAMP-Dependent Cytosolic Mislocalization of p27kip-Cyclin D1 During Quinol-Thioether–Induced Tuberous Sclerosis Renal Cell Carcinoma

The loss of tuberin, the tuberous sclerosis-2 (Tsc-2) gene product, is associated with cytoplasmic mislocalization of p27 in uterine leiomyomas derived from Eker rats (Tsc-2(EK/+)) and in human metastatic renal cell carcinoma tissue. Signaling associated with cytoplasmic mislocalization of p27 in renal cancer is relatively unknown. Renal tumors derived from 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ)-treated Tsc-2(EK/+) rats, and null for tuberin, display elevated nuclear and cytosolic p27, with parallel increases in cytosolic cyclin D1 levels. Similar changes are observed in TGHQ-transformed renal epithelial cells derived from Tsc-2(EK/+) rats (QTRRE cells), which, in addition to the cytoplasmic mislocalization of p27 and cyclin D1, exhibit high ERK, B-Raf, and Raf-1 kinase activity. Renal tumor xenografts, derived from subcutaneous injection of QTRRE cells into nude mice, also display increases in cytosolic mislocalization of p27 and cyclin D1. Dibutyryl cAMP and/or phosphodiesterase inhibitors (PIs; pentoxifylline or theophylline) increase Rap1B activation, B-Raf kinase activity, and cytosolic p27/cyclin D1 protein levels in QTRRE cells. Inhibition of Raf kinases with either sorafenib or B-Raf small interfering RNA (siRNA) caused a mitogen-activated protein kinase-mediated downregulation of p27. Moreover, decreases in cyclin D1 were also associated with p27 siRNA knockdown in QTRRE cells. Finally, theophylline-mediated increases in p27 and cyclin D1 were attenuated by sorafenib, which modulated Raf/MEK/ERK signaling. Collectively, these data suggest that the cAMP/Rap1B/B-Raf pathway modulates the expression of p27 and the cytoplasmic mislocalization of p27-cyclin D1 in tuberous sclerosis gene-regulated-renal cancer. Therefore, the loss of tuberin and engagement of the cAMP pathway may independently direct p27-cyclin D1 cytosolic stabilization during renal tumor formation.

P27 Is Mislocalized to the Cytoplasm by BCR-ABL In a Kinase-Independent Manner and Contributes to Leukemogenesis

AbstractAbstract 512 Background:BCR-ABL promotes cell cycle progression by interfering with the regulatory functions of p27, a cyclin dependent kinase (Cdk) inhibitor and tumor suppressor. We have previously shown that BCR-ABL kinase activity promotes degradation of nuclear p27 (Agarwal, A. et al. Blood 2008). Additionally, in primary CML cells, p27 is mislocalized to the cytoplasm, thereby relieving Cdks from p27 inhibition. Results from studies of solid tumors show that cytoplasmic p27 can actively contribute to oncogenesis, raising the question of whether cytoplasmic p27 in CML cells may actively promote leukemogenesis rather than merely compromise Cdk inhibition. We hypothesize that BCR-ABL disrupts p27 function in a dual manner by reducing nuclear p27, where p27 normally serves as a tumor suppressor, and by increasing cytoplasmic p27, where it might have oncogenic activity. Experimental Approach and Results:Immunoblotting of nuclear and cytoplasmic lysates of CD34+ cells from 11 CML patients revealed that p27 localization is predominantly cytoplasmic in the majority of patients (10/11; 91%) irrespective of disease phase, while p27 was mostly nuclear in normal controls. Similar results were obtained by immunofluorescence microscopy. Imatinib treatment increased nuclear p27 suggesting that nuclear p27 levels are regulated by BCR-ABL kinase activity. However, imatinib does not alter cytoplasmic p27 levels, suggesting that cytoplasmic mislocalization of p27 is a kinase-independent effect of BCR-ABL. Kinase-independent regulation of cytoplasmic p27 localization was also tested by immunofluorescence microscopy of p27−/− MEFs engineered to express active or kinase-dead BCR-ABL in combination with wild-type p27. In these cells cytoplasmic p27 abundance was increased both by kinase-active or kinase-dead BCR-ABL as compared to the vector control. To interrogate the role of p27 in vivo we retrovirally transduced p27+/+ or p27−/− bone marrow with BCR-ABL-GFP retrovirus and sorted Lin-/c-Kit+/Sca-I+ cells by FACS, allowing for injection of exactly matched numbers of BCR-ABL-expressing GFP+ cells (5000/animal). Median survival was significantly reduced for recipients of p27−/− marrow as compared to p27+/+ controls (34 days vs. 93 days p<0.0001). Recipients of p27−/− marrow also exhibited significantly increased white blood cell (4.5-fold) and platelet counts (3.9-fold) as well as spleen size (6-fold) and liver size (1.6-fold). Accordingly, there was more pronounced leukemic infiltration of myeloid precursors on histopathology as compared to controls. An in vivo competition experiment performed by injecting equal numbers of BCR-ABL-transduced p27−/− and p27+/+ marrow cells in congenic recipients resulted in leukemias in recipient mice (N=8) that were derived exclusively from p27−/− cells. In total, these results suggest that the net function of p27 in CML is tumor suppressive. To functionally dissect the role of nuclear and cytoplasmic p27, we used p27T187A transgenic mice (in which nuclear p27 degradation is reduced) and p27S10A mice (in which p27 export to the cytoplasm is reduced resulting in predominantly nuclear p27). Mice of matched genetic background were used as p27WT controls in CML retroviral transduction/transplantation experiments. In both cases, survival was prolonged compared to controls: 25 vs. 21 days for p27T187A (p=0.05) and 32 vs. 23 days for p27S10A (p=0.01). This suggests that stabilization of nuclear p27 (p27T187A) and more significantly lack of cytoplasmic p27 (p27S10A) attenuate BCR-ABL-mediated leukemogenesis. Consistent with this, autopsy and histopathological analysis revealed reduced hepatosplenomegaly (p27T187A mice) and improved cell differentiation with a relative increase of mature neutophils (p27S10A mice) as compared to wild-type controls. Conclusions:These results provide in vivo evidence that p27 has genetically separable dual roles in CML as both a nuclear tumor suppressor and cytoplasmic oncogene. A kinase-independent activity of BCR-ABL contributes to leukemogenesis through aberrant p27 localization to the cytoplasm. This oncogene activity is independent from the kinase-dependent degradation of nuclear p27. We speculate that the inability of tyrosine kinase inhibitors to reverse cytoplasmic p27 mislocalization may contribute to disease persistence despite effective inhibition of BCR-ABL kinase activity. Disclosures:Deininger:Novartis: Consultancy; BMS: Consultancy; Ariad: Consultancy; genzyme: Research Funding.

Abstract 5137: The PI3K pathway regulates the actin cytoskeleton, tumor cell migration and metastasis via the atypical tumor suppressor p27

Abstract The CDK inhibitor p27 plays a well-established role in cell cycle progression, regulating the G1-S phase transition. A growing body of evidence indicates a potential role for p27 as a mediator of tumor cell motility and invasiveness. The present data provides additional evidence for p27 as a mediator of cancer metastasis. These activities appear to require cytoplasmic mislocalization, and are independent of p27's action on CDKs and the cell cycle. p27 phosphorylation at T157 and T198 is mediated by the AGC kinases RSK, SGK, and AKT to promote cytoplasmic mislocalization and facilitate p27 binding to the RhoA cytoskeletal regulatory protein. p27-mediated inhibition of RhoA/ROCK signaling is associated with dynamic rearrangement of the actin cytoskeleton and increased cell migration and invasion. Overexpression of the PI3K effectors RSK, SGK, and mTOR all promote cytoplasmic mislocalization of p27, increased p27: RhoA binding, and all enhance directed cell migration as assayed by modified transwell assay. This increased tumor cell motility is dependent upon p27, as shRNA-mediated p27 knockdown reverts transwell invasion to parental levels. Overexpression of mTOR or these AGC kinases reduces cellular levels of RhoA-GTP and p-cofilin, both of which revert following shRNA p27 treatment. The increased p27: RhoA binding, decreased RhoA-GTP, and decreased p-cofilin correlate with dramatic loss of polymerized actin filaments as assayed by phalloidin staining, and all of these effects are rescued by shRNA p27. The in vivo relevance of these findings has been pursued in the highly metastatic human breast cancer sub-lines MDA-MB-231-1833 (bone-tropic) and MDA-MB-231-4175 (lung-tropic). Both highly metastatic variants demonstrate hyperactivation of the PI3K effectors SGK, RSK, and AKT relative to the parental MDA-MB-231 line and show markedly elevated p27 levels, with a shift in p27 protein localization to the cytoplasm, increased p27: RhoA binding, decreased p27-dependent levels of RhoA-GTP and p-cofilin, and increased p27-dependent invasiveness by modified transwell assay. The cell cycle profiles of MDA-MB-231-4175 and 1833 variants were unchanged by shRNA p27 supporting the notion that cytoskeletal effects of p27 in these lines are independent of cell cycle/Cdk regulatory activity. Of particular interest, the increase in lung tumor formation by MDA-MB-231-4175 following tail vein injection was strikingly reduced to near-parental levels after shRNA-mediated knockdown of p27. These results support a model whereby PI3K activation promotes p27 phosphorylation, mislocalization to the cytoplasm, enhanced RhoA binding and subsequent remodeling of the actin cytoskeleton. This cascade of events may be a major route whereby oncogenic PI3K activation mediates tumor cell acquisition of the invasive potential necessary for overt metastasis in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5137.

CAMP‐dependent pathway(s) directs the B‐Raf MAPK‐Mediated Cytosolic Mislocalization of p27kip‐cyclin D1 in Renal Cancer

The loss of tuberin, the tuberous sclerosis‐2 (Tsc‐2) gene product, is associated with cytoplasmic mislocalization of p27 in uterine leiomyomas derived from Eker rats (Tsc‐2EK/+), and has been recently observed in human renal cell carcinoma tissue. Signaling associated with the expression and cytoplasmic mislocalization of p27 is relatively unknown in renal tumor development. TGHQ transformed renal epithelial cells derived from Tsc‐2EK/+ rats (QTRRE cells), that form renal tumors in nude mice, display cytoplasmic mislocalization of p27 and cyclin D1, and also exhibit high ERK, B‐Raf and Raf‐1 kinase activity. Dibutyryl cAMP or phosphodiesterase inhibitors ([PIs]; pentoxifylline or theophylline) cause an increase in cytosolic p27/cyclin D1 protein levels in QTRRE cells. Additionally, treatment of QTRRE cells with both PIs revealed concomitant decreases in p‐p27 T187 and in its E3 ubiquitin ligase skp1; proteosome inhibition resulted in increased p27/cyclin D1 protein levels. Inhibition of Raf kinases with either sorafenib or B‐Raf siRNA resulted in MAPK down‐regulation of p27. Moreover, an associated decrease in cyclin D1 was observed following p27 siRNA knockdown in QTRRE cells. Collectively these data suggest that the cAMP/B‐Raf pathway modulates the expression of p27 and the cytoplasmic mislocalization of p27‐cyclin D1 in tuberous sclerosis‐gene regulated‐renal cancer. Therefore, the loss of tuberin and engagement of the cAMP pathway may independently direct p27‐cyclin D1 cytosolic stabilization during renal tumor formation.

The Oncogenic Role of Tumor Suppressor Protein p27 in Ph+ Chronic Myeloid Leukemia.

Abstract 3276Poster Board III-1 Background:Several studies have indicated that BCR-ABL causes cell cycle defects by interfering with the cell cycle regulatory functions of p27, a Cyclin dependent kinase (Cdk) inhibitor and tumor suppressor. Studies in BCR-ABL positive cell lines have shown that BCR-ABL promotes proteasomal degradation of p27 in a pathway that involves the SCFSKP2 ubiquitin ligase, while cytoplasmic mislocalization has been described in primary CML cells. It has been suggested that the principal effect of this cytoplasmic mislocalization is to remove p27 from the nucleus, thereby relieving Cdks from p27 inhibition. However, recent studies have shown that a p27 mutant (p27CK-), that cannot bind to Cdks or Cyclins, actively contributes to oncogenesis. This raises the question as to whether cytoplasmic mislocalization of p27 in CML cells may in fact promote leukemogenesis rather than merely compromise Cdk inhibition. We therefore hypothesized that the net contribution of p27 in CML is to promote leukemogenesis due to the oncogenic activity of cytoplasmic p27. Experimental approach and results:We determined p27 localization in BCR-ABL positive cell lines and CD34+ progenitor cells from newly diagnosed chronic phase CML patients (N=7) and from CML patients in blast crisis (N=2) by immunoblotting of nuclear and cytoplasmic cellular fractions. We found that p27 is predominantly cytoplasmic in most CML cell lines and in CD34+ cells from 8/9 (89%) patient samples, including patients in blastic phase. Cytoplasmic localization of p27 in CD34+ cells from CML patients was also confirmed by immunofluorescence analysis. Further, we observed that inhibition of BCR-ABL kinase by imatinib, an Abl kinase inhibitor increased nuclear p27 in all cell lines tested and in 4/9 patient samples (3/7 chronic phase and 1/2 blastic phase samples). However, we did not observe a substantial change in the cytoplasmic p27 levels. Similar results were obtained in Ba/F3 and 32D murine hematopoietic cell lines expressing BCR-ABL when compared with the respective parental cells. Further, SKP2 was up-regulated in CD34+ cell from CML patients as compared to the normal patients consistent withSKP2 mediated down-regulation of nuclear p27. These data suggest that nuclear but not cytoplasmic p27 levels are predominantly regulated by BCR-ABL kinase activity. To test whether p27 is crucial for BCR-ABL-driven leukemia, we compared leukemogenesis between recipients of BCR-ABL transduced p27+/+ and p27-/- bone marrow. Mice transplanted with BCR-ABL infected p27-/- marrow had significantly longer median survival (70 days, range 48-150 days) compared to recipients of p27+/+ marrow (37 days, range 14-56 days) (p=0.0123). To exclude that this difference was related to the differences in homing and engraftment capabilities of p27+/+ and p27-/- bone marrow cells, we compared short term homing and long term engraftment of p27+/+ and p27-/- bone marrow cells transplanted into wild-type recipients and found no differences. These data suggest that the net contribution of p27 to BCR-ABL-mediated leukemogenesis is positive. Further, to investigate the contribution of nuclear p27 to leukemogenesis, we utilized marrow from p27S10A mice in the murine CML model. In p27S10A mice, p27 is nuclear to to abrogation of the phosphorylation site implicated in nuclear export. We injected BCR-ABL transduced bone marrow cells of p27S10A and p27+/+ mice into wild-type recipients and compared the disease progression. We observed that mice transplanted with BCR-ABL infected p27S10A marrow had significantly longer median survival (28 days, range 23-79 days) compared to the recipients of p27+/+ marrow (23 days, range 21-38 days) (p=0.0139). This data is consistent with nuclear tumor suppressor function of p27. Combined with the data above, this suggests that cytoplasmic p27 promotes BCR-ABL mediated leukemogenesis. Conclusions:Our data suggest that though nuclear p27 functions as a tumor suppressor, the net contribution of p27 in CML might be oncogenic due to an oncogenic role of the increased cytoplasmic p27. Restoring nuclear p27 or reducing cytoplasmic p27 may be therapeutically useful in malignancies with low nuclear and high cytoplasmic p27 expression. Disclosures:Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. Deininger:Genzyme: Research Funding; BMS: Consultancy; Novartis: Consultancy, Honoraria; Ariad : Research Funding.

Cytoplasmic Sequestration of p27 via AKT Phosphorylation in Renal Cell Carcinoma

p27 localization and expression has prognostic and predictive value in cancer. Little is known regarding expression patterns of p27 in renal cell carcinoma (RCC) or how p27 participates in disease progression or response to therapy. RCC-derived cell lines, primary tumors, and normal renal epithelial cells were analyzed for p27 expression, phosphorylation (T157 of the NLS), and subcellular localization. RCC-derived cell lines were treated with phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors and effects on p27 localization were assessed. The potential contribution of cytoplasmic p27 to resistance to apoptosis was also evaluated. p27 was elevated in tumors compared with matched controls, and cytoplasmic mislocalization of p27 was associated with increasing tumor grade. Cytoplasmic localization of p27 correlated with phosphorylation at T157, an AKT phosphorylation site in the p27 NLS. In RCC cell lines, activated PI3K/AKT signaling was accompanied by mislocalization of p27. AKT activation and phosphorylation of p27 was associated with resistance to apoptosis, and small interfering RNA knockdown of p27 or relocalization to the nucleus increased apoptosis in RCC cells. Treatment with the PI3K inhibitors LY294002 or wortmannin resulted in nuclear relocalization of p27, whereas mTOR inhibition by rapamycin did not. In RCC, p27 is phosphorylated at T157 of the NLS, with increasing tumor grade associated with cytoplasmic p27. PI3K inhibition (which reduces AKT activity) reduces T157 phosphorylation and induces nuclear relocalization of p27, whereas mTOR inhibition does not. Clinical testing of these findings may provide a rational approach for use of mTOR and PI3K/AKT pathway inhibitors in patients with RCC.

AMP-activated protein kinase signaling results in cytoplasmic sequestration of p27.

Tuberin, the Tsc2 gene product, integrates the phosphatidylinositol 3-kinase/mitogen-activated protein kinase (mitogenic) and LKB1/AMP-activated protein kinase (AMPK; energy) signaling pathways, and previous independent studies have shown that loss of tuberin is associated with elevated AMPK signaling and altered p27 function. In Tsc2-null tumors and tumor-derived cells from Eker rats, we observed elevated AMPK signaling and concordant cytoplasmic mislocalization of p27. Cytoplasmic localization of p27 in Tsc2-null cells was reversible pharmacologically using inhibitors of the LKB1/AMPK pathway, and localization of p27 to the cytoplasm could be induced directly by activating AMPK physiologically (glucose deprivation) or genetically (constitutively active AMPK) in Tsc2-proficient cells. Furthermore, AMPK phosphorylated p27 in vitro on at least three sites including T170 near the nuclear localization signal, and T170 was shown to determine p27 localization in response to AMPK signaling. p27 functions in the nucleus to suppress cyclin-dependent kinase-2 (Cdk2) activity and has been reported to mediate an antiapoptotic function when localized to the cytoplasm. We found that cells with elevated AMPK signaling and cytoplasmic p27 localization exhibited elevated Cdk2 activity, which could be suppressed by inhibiting AMPK signaling. In addition, cells with elevated AMPK signaling and cytoplasmic p27 localization were resistant to apoptosis, which could be overcome by inhibition of AMPK signaling and relocalization of p27 to the nucleus. These data show that AMPK signaling determines the subcellular localization of p27, and identifies loss of integration of pathways controlling energy balance, the cell cycle, and apoptosis due to aberrant AMPK and p27 function as a feature of cells that have lost the Tsc2 tumor suppressor gene.

Cytoplasmic localization of p27 (cyclin-dependent kinase inhibitor 1B/KIP1) in colorectal cancer: inverse correlations with nuclear p27 loss, microsatellite instability, and CpG island methylator phenotype

Cytoplasmic mislocalization of p27 (CDKN1B/KIP1) is caused by activated AKT1 and has been associated with poor prognosis in various cancers. CIMP in colorectal cancer is characterized by extensive promoter methylation and is associated with MSI-MSI-H and BRAF mutations. We have recently shown a positive correlation between MSI/CIMP and loss of nuclear p27. However, no study has examined cytoplasmic p27 mislocalization in relation to CIMP and MSI in colorectal cancer. Using MethyLight assays, we quantified DNA methylation in 8 CIMP-specific gene promoters (CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1) in 853 colorectal cancer samples obtained from 2 large prospective cohorts. We assessed expressions of nuclear and cytoplasmic p27 and nuclear p53 by immunohistochemistry. Cytoplasmic p27 expression was inversely associated with loss of nuclear p27 (P < .0001), CIMP-high (P < .0001), MSI-H (P < .0001), and BRAF mutations (P < .0001). The inverse association of cytoplasmic p27 with CIMP-high (or MSI-H) was independent of MSI (or CIMP) status. In addition, the inverse association of cytoplasmic p27 with CIMP-high was independent of KRAS/BRAF status. BRAF and CDKN2A (p16) methylation were not correlated with cytoplasmic p27 after stratification by CIMP status. The inverse associations of cytoplasmic p27 with MSI-H and CIMP-high were much more pronounced in p53-negative than p53-positive tumors. In conclusion, cytoplasmic p27 expression is inversely associated with MSI-H and CIMP-high, particularly in p53-negative tumors, suggesting interplay of functional losses of p27 and p53 in the development of various molecular subtypes of colorectal cancer.

A pathway in quiescent cells that controls p27Kip1 stability, subcellular localization, and tumor suppression.

We have created two knock-in mouse models to study the mechanisms that regulate p27 in normal cells and cause misregulation of p27 in tumors: p27(S10A), in which Ser10 is mutated to Ala; and p27(CK-), in which point mutations abrogate the ability of p27 to bind cyclins and CDKs. These two mutant alleles identify steps in a pathway that controls the proteasomal degradation of p27 uniquely in quiescent cells: Dephosphorylation of p27 on Ser10 inhibits p27 nuclear export and promotes its assembly into cyclin-CDK complexes, which is, in turn, necessary for p27 turnover. We further show that Ras-dependent lung tumorigenesis is associated with increased phosphorylation on Ser10 and cytoplasmic mislocalization of p27. Indeed, we find that p27(S10A) is refractory to Ras-induced cytoplasmic translocation and that p27(S10A) mice are tumor resistant. Thus, phosphorylation of p27 on Ser10 is an important event in the regulation of the tumor suppressor function of p27.