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A feed-forward loop involving protein kinase Calpha and microRNAs regulates tumor cell cycle.

ABSTRACT: Protein kinase Calpha (PKCalpha) has been implicated in cancer, but the mechanism is largely unknown. Here, we show that PKCalpha promotes head and neck squamous cell carcinoma (SCCHN) by a feed-forward network leading to cell cycle deregulation. PKCalpha inhibitors decrease proliferation in SCCHN cell lines and xenografted tumors. PKCalpha inhibition or depletion in tumor cells decreases DNA synthesis by suppressing extracellular signal-regulated kinase phosphorylation and cyclin E synthesis. Additionally, PKCalpha down-regulates miR-15a, a microRNA that directly inhibits protein synthesis of cyclin E, as well as other cell cycle regulators. Furthermore, both PKCalpha and cyclin E protein expression are increased in primary tumors, and PKCalpha inversely correlates with miR-15a expression in primary tumors. Finally, PKCalpha is associated with poor prognosis in SCCHN. These results identify PKCalpha as a key regulator of SCCHN tumor cell growth by a mechanism involving activation of mitogen-activated protein kinase, an initiator of the cell cycle, and suppression of miR-15a, an inhibitor of DNA synthesis. Although the specific components may be different, this type of feed-forward loop network, consisting of a stimulus that activates a positive signal and removes a negative brake, is likely to be a general one that enables induction of DNA synthesis by a variety of growth or oncogenic stimuli.

SUBMITTER: Cohen EE

PROVIDER: S-EPMC2746005 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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A feed-forward loop involving protein kinase Calpha and microRNAs regulates tumor cell cycle.

Cohen Ezra E W EE Zhu Hongyan H Lingen Mark W MW Martin Leslie E LE Kuo Wen-Liang WL Choi Eugene A EA Kocherginsky Masha M Parker Joel S JS Chung Christine H CH Rosner Marsha Rich MR

Cancer research 20090101 1

Protein kinase Calpha (PKCalpha) has been implicated in cancer, but the mechanism is largely unknown. Here, we show that PKCalpha promotes head and neck squamous cell carcinoma (SCCHN) by a feed-forward network leading to cell cycle deregulation. PKCalpha inhibitors decrease proliferation in SCCHN cell lines and xenografted tumors. PKCalpha inhibition or depletion in tumor cells decreases DNA synthesis by suppressing extracellular signal-regulated kinase phosphorylation and cyclin E synthesis. A ...[more]

PMID: 19117988

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Project description:The small GTPase RAC1B functions as a powerful inhibitor of transforming growth factor (TGF)-β1-induced epithelial-mesenchymal transition, cell motility, and growth arrest in pancreatic epithelial cells. Previous work has shown that RAC1B downregulates the TGF-β type I receptor ALK5, but the molecular details of this process have remained unclear. Here, we hypothesized that RAC1B-mediated suppression of activin receptor-like kinase 5 (ALK5) involves proteinase-activated receptor 2 (PAR2), a G protein-coupled receptor encoded by F2RL1 that is crucial for sustaining ALK5 expression. We found in pancreatic carcinoma Panc1 cells that PAR2 is upregulated by TGF-β1 in an ALK5-dependent manner and that siRNA-mediated knockdown of RAC1B increased both basal and TGF-β1-induced expression of PAR2. Further, the simultaneous knockdown of PAR2 and RAC1B rescued Panc1 cells from a RAC1B knockdown-induced increase in ALK5 abundance and the ALK5-mediated increase in TGF-β1-induced migratory activity. Conversely, Panc1 cells with stable ectopic expression of RAC1B displayed reduced ALK5 expression, an impaired upregulation of PAR2, and a reduced migratory responsiveness to TGF-β1 stimulation. However, these effects could be reversed by ectopic overexpression of PAR2. Moreover, the knockdown of PAR2 alone in Panc1 cells and HaCaT keratinocytes phenocopied RAC1B's ability to suppress ALK5 abundance and TGF-β1-induced chemokinesis and growth inhibition. Lastly, we found that the RAC1B knockdown-induced increase in TGF-β1-induced PAR2 mRNA expression was sensitive to pharmacological inhibition of MEK-ERK signaling. Our data show that in pancreatic and skin epithelial cells, downregulation of ALK5 activity by RAC1B is secondary to suppression of F2RL1/PAR2 expression. Since F2RL1 itself is a TGF-β target gene and its upregulation by TGF-β1 is mediated by ALK5 and MEK-ERK signaling, we suggest the existence of a feed-forward signaling loop involving ALK5 and PAR2 that is efficiently suppressed by RAC1B to restrict TGF-β-driven cell motility and growth inhibition.

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A feed-forward loop involving protein kinase Calpha and microRNAs regulates tumor cell cycle.

Publications

A feed-forward loop involving protein kinase Calpha and microRNAs regulates tumor cell cycle.

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