PPM1A Expression Research Articles

Abstract 2857: Induced expression of DUSP4 and PPM1A in ER-negative breast cancer cells suppresses proliferation and invasion

Abstract Background: ER-negative breast cancers are poor prognosis tumors that occur more commonly in young women. Current treatments for ER-negative tumors include cytotoxic chemotherapy, or for those ER-negative breast cancers that overexpress HER2, the anti-HER2 antibody herceptin. Targeted therapy for ER-negative tumors, particularly those that do not express HER2 (“triple-negative breast cancer”) is urgently needed. We previously identified kinases that are critical for the growth of “triple-negative” breast cancer. In this project, we investigated whether phosphatases are differentially expressed in ER-negative as compared to ER-positive breast cancers. We hypothesized that: (1) the specific phosphatases that govern the growth of ER-negative cancers are different from those of ER-positive cancers, (2) Induced expression of those phosphatases that are lowly expressed in ER-negative breast cancers will suppress the growth and invasion of ER-negative breast cancers. Methods: Using 277 human breast tumors (56 ER-positive and 221 ER-negative) from the Baylor Breast Center tumor bank, we isolated RNA and performed Affymetrix microarray studies. cDNA was synthesized and Biotin-labeled and was then hybridized onto an Affymetrix HGU133A GeneChipTM, comprised of 22,000 genes. Statistical analysis of phosphatases was done with dChip software, and phosphatases more highly (>1.5 fold; FDR=0.05) or lowly (<0.66-fold; FDR=0.05) expressed in ER-negative breast cancers as compared to ER-positive breast cancers were selected for further study. Over expression of DUSP4 and PPM1A in breast cancer cells was achieved using a Tet-regulated pUHD vector (Tet Off System). Cell growth was measured by MTS assay. Soft agar and invasion assays were performed using previously published protocols. Results: We identified 20 highly-expressed (>1.5 fold; FDR=0.05), and 29 lowly-expressed (<0.66-fold; FDR=0.05) phosphatases in ER-negative human breast cancers. We selected two lowly expressed phosphatases (DUSP4 and PPM1A) for further study. Induced expression of DUSP4 and PPM1A in ER-negative MDA-MB-468 cells inhibited anchorage-dependent and -independent growth. Induced expression of DUSP4 and PPM1A also suppressed the invasion of MDA-MB-468 cells. We are currently investigating the cellular and molecular consequences of induced DUSP4 and PPM1A expression in other ER-negative and ER-positive breast cancer cell lines. Conclusion: We identified a set of highly expressed and lowly expressed phosphatases in ER-negative breast cancers as compared to ER-positive cancers. Two phosphatases (DUSP4 and PPM1A) when expressed in an ER-negative breast cancer cells inhibit growth and invasion of these cells. By identifying the molecules that regulate breast cancer cell growth we will identify potential new targets for the treatment of these aggressive ER-negative breast cancers. 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 2857. doi:1538-7445.AM2012-2857

Expression and significance of LMP2 and PPM1A in gestational trophoblastic disease

To investigate the expression of low molecular mass polypeptide-2 (LMP2) and protein phosphatase 1A (PPM1A) in gestational trophoblastic disease and elucidate their predictive value in malignant transformation of hydatidiform mole. The expressions of LMP2 and PPM1A protein in 196 complete hydatidiform moles (in which 28 cases with malignant transformation), 7 invasive moles, 5 choriocarcinomas and 20 normal chorionic villus were detected with the method of EnVision immunohistochemistry. Their clinicopathologic data were retrospectively analyzed. LMP2 and PPM1A protein expressed in cytotrophocytes, syncytiotrophoblast and extravillous trophoblast. The level of LMP2 expression in deteriorative hydatidiform mole was significantly higher than that in non-deteriorative hydatidiform mole or normal chorionic villus (6.79±2.38, 5.26±2.63 and 3.10±1.65, all P<0.01), while there were no difference compared with gestational trophoblastic neoplasms (6.42±2.68, P=0.113). The level of PPM1A expression was highest in normal chorionic villus, and decreased gradually in hydatidiform mole (non-deteriorative and deteriorative) and gestational trophoblastic neoplasms (6.30±2.98, 4.93±2.50, 4.43±2.04 and 3.33±2.06, all P<0.01); the level of PPM1A expression in deteriorative hydatidiform mole was significantly lower than that in non-deteriorative hydatidiform mole (P=0.001). The expression of LMP2 protein was correlated to theca lutein ovarian cyst, the expression of PPM1A protein was related with uterine size (P<0.05). While, there was no correlation between the expressions of the two proteins (P>0.05). High expression of LMP2 and low expression of PPM1A might play an important role in the motility and invasiveness of trophoblast cells and malignant transformation of hydatidiform mole. Testing the expression of LMP2 and PPM1A in hydatidiform mole tissues of initial uterine evacuation might be have some reference significance in judging outcomes of hydatidiform mole.

PPM1A and PPM1B act as IKKβ phosphatases to terminate TNFα-induced IKKβ-NF-κB activation

IKKβ serves as a central intermediate signaling molecule in the activation of the NF-κB pathway. However, the precise mechanism for the termination of IKKβ activity is still not fully understood. Using a functional genomic approach, we have identified two protein serine/threonine phosphatases, PPM1A and PPM1B, as IKKβ phosphatases. Overexpression of PPM1A or PPM1B results in dephosphorylation of IKKβ at Ser177 and Ser181 and termination of IKKβ-induced NF-κB activation. PPM1A and PPM1B associate with the phosphorylated form of IKKβ, and the interaction between PPM1A/PPM1B and IKKβ is induced by TNFα in a transient fashion in the cells. Furthermore, knockdown of PPM1A and PPM1B expression enhances TNFα-induced IKKβ phosphorylation, NF-κB nuclear translocation and NF-κB-dependent gene expression. These data suggest that PPM1A and PPM1B play an important role in the termination of TNFα-mediated NF-κB activation through dephosphorylating and inactivating IKKβ.

Protein Serine/Threonine Phosphatase PPM1A Dephosphorylates Smad1 in the Bone Morphogenetic Protein Signaling Pathway

Bone morphogenetic proteins (BMPs) are secreted polypeptides belonging to the transforming growth factor-beta (TGF-beta) superfamily that activates a broad range of biological responses in the metazoan organism. The BMP-initiated signaling pathway is under tight control by processes including regulation of the ligands, the receptors, and the key downstream intracellular effector Smads. A critical point of control in BMP signaling is the phosphorylation of Smad1, Smad5, and Smad8 in their C-terminal SXS motif. Although such phosphorylation, which is mediated by the type I BMP receptor kinases in response to BMP stimulation, is well characterized, biochemical mechanisms underlying Smad dephosphorylation remain to be elucidated. In this study, we have found that PPM1A, a metal ion-dependent protein serine/threonine phosphatase, physically interacts with and dephosphorylates Smad1 both in vitro and in vivo. Functionally, overexpression of PPM1A abolishes BMP-induced transcriptional responses, whereas RNA interference-mediated knockdown of PPM1A enhances BMP signaling. Collectively, our study suggests that PPM1A plays an important role in controlling BMP signaling through catalyzing Smad dephosphorylation.