Role Of Salt-inducible Kinases Research Articles

Salt-inducible kinases (SIKs) in cancer: mechanisms of action and therapeutic prospects.

Salt-inducible kinases (SIKs), a group of serine/threonine kinases in the adenosine monophosphate-activated protein kinase (AMPK) family, exist in three isoforms: SIK1, SIK2 and SIK3. These kinases are crucial in various physiological processes. Emerging evidence indicates that dysregulation of SIK expression and activation significantly contributes to carcinogenesis by promoting cellular proliferation, metabolic dysregulation, metastasis and chemoresistance through the modulation of crucial signaling pathways. The role of SIKs in cancer progression and metastasis involves complex mechanisms that vary among cancer types. Additionally, research on SIK inhibitors suggests that targeting these kinases might offer promising avenues for improving cancer treatment outcomes.

The role of salt-inducible kinases on the modulation of renal and intestinal Na+,K+-ATPase activity during short- and long-term high-salt intake

Type 1 salt-inducible kinases (SIK1) has been shown to act as a mediator during the cellular adaptation to variations in intracellular sodium in a variety of cell types. Type 2 SIK (SIK2) modulates various biological functions and acts as a signal transmitter in various pathways. To evaluate the role of both SIK isoforms in renal and intestinal Na+,K+-ATPase (NKA) activity, we made use of constitutive sik1−/− (SIK1–KO), sik2−/− (SIK2–KO), double sik1−/−sik2−/− (double SIK1*2-KO) knockout and wild-type (WT) mice challenged to a standard (0.3% NaCl) or chronic high-salt (HS, 8% NaCl) diet intake for 48 h or 12 weeks.Long-term HS intake in WT was accompanied by 2-fold increase in jejunal NKA activity and slight (~30% reduction) decreases in NKA in the ileum and cecum; none of these changes was accompanied by changes in the expression of α1-NKA. The ablation of SIK1 and SIK2 prevented the marked increase in jejunal NKA activity following the long-term HS intake. The ablation of SIK1 and SIK2 in mice on a long-term HS intake impacted differently in the ileum and cecum. The most interesting finding is that in SIK2–KO mice marked reductions in NKA activity were observed in the ileum and cecum when compared to WT mice, both on normal and long-term HS intake.In summary, SIK1 or SIK2 ablation on chronic high-salt intake is accompanied by modulation of NKA along the intestinal tract, which differ from those after an acute high-salt intake, and this may represent an absorptive compensatory mechanism to keep electrolyte homeostasis.

Abstract PS4-41: Salt-inducible kinases suppress tumour function and regulate drug resistance in breast cancer

Abstract Background: Salt-inducible kinases (SIKs) belonging to an AMP-activated kinase (AMPK) family, have functions in tumourgeniesis and metastasis in many solid tumours. However, the role of SIKs in breast cancer is not clear. In this study we aimed to determine the function of SIKs (SIK1, SIK2 and SIK3) in human breast cancer. Method: A cohort of breast cancer tissues (n=102) were analysed using qPCR to determine changes in SIK expression (SIK1, SIK2, SIK3 and housekeeping GAPDH ) between cancer and normal tissues and different aetiologies of cancer. In addition, a breast disease spectrum array (TMA) was probed for SIK expression at the protein level. SIK1, 2 and 3 were knocked down using shRNA in the human breast cancer cell lines MCF-7 and MDA-MB-231 and changes in cell behaviour were assessed using a number of cell function assays.Results: At the messenger level, expression of SIK2 was lower in breast cancer than normal tissue (p=0.0179), while expression of SIK1 and SIK3 had no significant difference between breast cancer and normal tissue. SIK3 expression was associated with ER status in the cohort (p=0.02). The level of SIK2 expression was significantly different in Stage I and Stage III. While SIK3 expression was significantly higher in ER positive breast cancer than ER negative breast cancer. Further analysis using Kaplan-Meier survival was performed for SIKs expression in an online database (http://kmplot.com/analysis/index.php?p=background) which showed that that an increased expression of SIKs was associated with good prognosis in the breast cancer cohort (p<0.01). Moreover, IHC staining correlation of SIKs in tumour with different clinicopathological characteristics showed a SIK1 Klein score significantly higher in ER positive breast cancer than ER negative breast cancer; in SIK3, a higher Klein score was observed in breast cancer with higher Grade, negative lymph node and higher TNM stage (p <0.05). In vitro, reduced expression of SIK2 and SIK3 increases the proliferation of breast cancer cells. However, SIK2 and SIK3 had differential effects on breast cancer cell adhesion. Knockdown of SIK2 only enhanced the adhesion of triple negative breast cancer cells (MDA-MB-231), while knockdown of SIK3 decreased the adhesion of both MDA-MB-231 and MCF 7 cells. Knockdown of SIK1 and SIK3 increased the invasion of MDA-MB-231 cells (p<0.05). Knockdown SIK1 increased the barrier but knockdown of SIK2 and SIK3 decreased the barrier of the breast cancer cells (p<0.05). We also determined the effect of possible chemotherapeutic resistance in these cell lines: the cells were treated with various concentration of chemotherapy drugs and placebo and found that reduced SIKs increased the resistance of breast cancer cell to paclitaxel and cisplatin.Conclusion: In conclusion, we show that low expression of SIK1,2 and 3 in breast cancer was correlated with poor prognosis and chemotherapy resistance of breast cancer. Reduced SIKs promote tumour metastasis by enhancing tumour function and tight junction. SIKs could be potential biomarkers for prognosis and chemotherapy sensitivity in breast cancer. Citation Format: Ling Xin, Chang Liu, Yinhua Liu, Robert E. Mansel, Eleri Davies, Wen G. Jiang, Tracey A. Martin. Salt-inducible kinases suppress tumour function and regulate drug resistance in breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-41.

Role of salt inducible kinase 1 in high glucose-induced lipid accumulation in HepG2 cells and metformin intervention

AimsTo investigate the roles of salt inducible kinase (SIK1) in high glucose-induced triglyceride accumulation in human hepatoma HepG2 cells as well as in the molecular mechanism by which metformin, a drug to treat diabetes, suppresses high glucose-induced lipogenesis. Main methodsA cell model for high glucose-induced hepatic steatosis was prepared by exposing HepG2 cells to high glucose (25mmol) in the absence or presence of metformin (0.5mmol). Intracellular triglycerides were visualized by Oil Red O and measured using a triglyceride assay kit. Cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. SIK1 overexpression in HepG2 cells was achieved by transient transfection, and the mRNA and protein levels of SIK1 and lipogenic factors were measured using a reverse transcription-polymerase chain reaction and western blotting, respectively. Key findingsLipid accumulation in HepG2 cells was obvious after treatment with high glucose for 24h. In response to high glucose, SIK1 expression was negatively correlated with that of lipogenic factors and lipid accumulation in HepG2 cells. We observed that overexpression of SIK1, or treatment with metformin, suppressed lipogenesis, even in high glucose conditions. Furthermore, treatment with metformin upregulated SIK1 mRNA and protein levels, as well as the active form of SIK1. SignificanceSIK1 plays a vital role in high glucose-induced lipid accumulation, and metformin suppresses lipogenesis via the induction and activation of SIK1.

A Novel Role of Salt-Inducible Kinase 1 (SIK1) in the Post-Translational Regulation of Scavenger Receptor Class B Type 1 Activity.

Salt-inducible kinase 1 (SIK1) is a serine/threonine kinase that belongs to the stress- and energy-sensing AMPK family of kinases. SIK1 expression is rapidly induced in Y1 adrenal cells in response to ACTH via the cAMP-PKA signaling cascade, and it has been suggested that an increased level of SIK1 expression inhibits adrenal steroidogenesis by repressing the cAMP-dependent transcription of steroidogenic proteins, CYP11A1 and StAR, by attenuating CREB transcriptional activity. Here we show that SIK1 stimulates adrenal steroidogenesis by modulating the selective HDL-CE transport activity of SR-B1. Overexpression of SIK1 increases cAMP-stimulated and SR-B1-mediated selective HDL-BODIPY-CE uptake in cell lines without impacting SR-B1 protein levels, whereas knockdown of SIK1 attenuated cAMP-stimulated selective HDL-BODIPY-CE uptake. SIK1 forms a complex with SR-B1 by interacting with its cytoplasmic C-terminal domain, and in vitro kinase activity measurements indicate that SIK1 can phosphorylate the C-terminal domain of SR-B1. Among potential phosphorylation sites, SIK1-catalyzed phosphorylation of Ser496 is critical for SIK1 stimulation of the selective CE transport activity of SR-B1. Mutational studies further demonstrated that both the intact catalytic activity of SIK1 and its PKA-catalyzed phosphorylation are essential for SIK1 stimulation of SR-B1 activity. Finally, overexpression of SIK1 caused time-dependent increases in SR-B1-mediated and HDL-supported steroid production in Y1 cells; however, these effects were lost with knockdown of SR-B1. Taken together, these studies establish a role for SIK1 in the positive regulation of selective HDL-CE transport function of SR-B1 and steroidogenesis and suggest a potential mechanism for SIK1 signaling in modulating SR-B1-mediated selective CE uptake and associated steroidogenesis.

Abstract 1982: TGF-beta induced SIK cooperates with Smurf2 to negatively regulate type I receptor kinase signaling

Abstract Signal transduction pathways, like transforming growth factor beta (TGFβ), regulate many physiological processes and require control mechanisms to safeguard proper and timely action. Dysregulation of TGFβ signaling is established as a major player in cancer progression. We have recently described how negative regulation of TGFβ signaling is controlled by the serine/threonine kinase salt-inducible kinase (SIK). SIK is induced by TGFβ and forms protein complexes with the TGFβ type I receptor and with the inhibitory Smad7, which leads to type I receptor downregulation. We now investigate this mechanism further and demonstrate similarities between TGFβ/Smad-mediated immediate-early induction of SIK and Smad7. We also relate another protein of the negative feedback loop of TGFβ signaling, the E3 ubiquitin ligase Smurf2, to this mechanism of regulation. We provide evidence that Smurf2 cooperates with SIK to downregulate the type I receptor. Both the kinase activity of SIK and the ubiquitin ligase activity of Smurf2 are important for proper receptor turnover. However, Smurf2 does not directly bind to SIK, but participates in the complex via the PY-motif of Smad7. We thus establish a central role for Smad7 during SIK-mediated receptor downregulation. Finally, we explore the role of SIK in a cancer context by investigating its expression profile in human prostate cancer tissues. In conclusion, we have uncovered a phosphorylation/ubiquitination-dependent mechanism for TGFβ receptor downregulation that could play important roles during cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1982. doi:10.1158/1538-7445.AM2011-1982