Briefly, LOC441204 bound to β-catenin preventing its degradation, resulting in downstream p21 repression and cdk4 activation to enhance glioma cell proliferation.
More importantly, TMEM45A siRNA treatment significantly down-regulated the proteins promoting cell cycles transition (Cyclin D1, CDK4 and PCNA) and cell invasion (MMP-2 and MMP-9), which indicted a possible mechanism underlying its functions on glioma.
Here, we demonstrated that elevated CDK4 expression is correlated with poor prognosis in glioma after radiotherapy and that CDK4 knockdown conferred radiosensitivity in glioma cell lines.
This paper elucidates a model to regulate glioma cell cycle progression in which hUCBSC acts to control cyclin D1 induction and in concert its partner kinases, Cdk 4 and Cdk 6 by mediating cell cycle arrest at G(0)-G(1) phase.
Thus, whereas germ-line mutations of PTEN, p53, p16(INK4A)/p14(ARF), and CDK4 are not common events in familial glioma, outside of familial cancer syndromes, point mutations of p53 and hemizygous deletions and other rearrangements of the p16(INK4A)/p14(ARF) tumor suppressor region may account for a subset of familial glioma cases.
Thus, despite the association between the sporadic forms of high-grade glioma and abnormalities of p16(INK4A), p15(INK4B), or CDK4, we found no evidence that germ-line mutations in the coding region of these three genes predispose to inherited glial tumors.
Alterations in P16ink4 or in the gene encoding one of its ligands, cyclin-dependent kinase 4 (CDK4), have been reported in human glioma cell lines and primary tumors but not in primitive neuroectodermal tumors (PNETs), the most common malignant brain tumor of childhood.
Lack of p16INK4 or retinoblastoma protein (pRb), or amplification-associated overexpression of cdk4 is observed in distinct subsets of malignant glial tumors and cell lines.
These results suggest: (a) the involvement of P16INK4 in glioma progression; (b) that mechanisms other than mutation or deletion can down-regulate expression of the p16/CDKN2 gene; and (c) that the balance between CDK4 and its cognate inhibitor, P16INK4, may confer a cell growth advantage and facilitate tumor progression.
Here we have examined 32 glioma cell lines for amplification-associated overexpression of the CDK4 gene as an alternative mechanism for abrogating the growth-regulatory effects of p16.