Expression of p57KIP2 Potently Blocks the Growth of Human Astrocytomas and Induces Cell Senescence

Abstract

Astrocytic tumors frequently exhibit defects in the expression or activity of proteins that control cellcycle progression. Inhibition of kinase activity associated with cyclin/cyclin-dependent kinase co-complexes by cyclin-dependent kinase inhibitors is an important mechanism by which the effects of growth signals are down-regulated. We undertook the present study to determine the role of p57 KIP2 (p57) in human astrocytomas. We demonstrate here that whereas p57 is expressed in fetal brain tissue, specimens of astrocytomas of varying grade and permanent astrocytoma cell lines do not express p57, and do not contain mutations of the p57 gene by multiplex-heteroduplex analysis. However, the inducible expression of p57 in three well-characterized human astrocytoma cell lines (U343 MG-A, U87 MG, and U373 MG) using the tetracycline repressor system leads to a potent proliferative block in G 1 as determined by growth curve and flow cytometric analyses. After the induction of p57, retinoblastoma protein, p107, and E2F-1 levels diminish, and retinoblastoma protein is shifted to a hypophosphorylated form. Morphologically, p57-induced astrocytoma cells became large and flat with an expanded cytoplasm. The inducible expression of p57 leads to the accumulation of senescence-associated ␤-galactosidase marker within all astrocytoma cell lines such that ϳ75% of cells were positive at 1 week after induction. Induction of p57 in U373 astrocytoma cells generated a small population of cells (ϳ15%) that were nonviable, contained discrete nuclear fragments on The most common brain tumor is the astrocytoma accounting for ϳ65% of all primary brain tumors. The malignant astrocytoma has a very poor prognosis primarily because of its highly proliferative and invasive nature. As with other neoplasms with increased proliferative potential, malignant astrocytomas demonstrate dysregulation of various components of the cell cycle machinery. Altered expression of positive growth regulators such as growth factors, cyclins, and cyclin-dependent kinases (CDKs), or the loss of negative regulators, including cyclin-dependent kinase inhibitors (CKIs) and the retinoblastoma protein (pRB) have all been demonstrated in malignant astrocytomas. 1,2 The CDKs phosphorylate pRB to release cells from cell-cycle arrest. In contrast with CDKs, the CKIs inhibit cyclin-CDK complexes and transduce internal or external growth suppressive signals. Accordingly, all CKIs may be construed as candidate tumor suppressor genes.The CKIs are divided into two families, the INK4 and the CIP/KIP, which are defined on the basis of their structural homology and mechanism of action. The CIP/KIP family includes three structurally related members, p21 CIP1/WAF1 , 3,4 p27 KIP1 , 5,6 and a recently isolated and cloned third member, p57 KIP2 (p57). 7-10 These three CKIs share a common N-terminal domain for binding to and inhibiting the kinase activity of CDK-cyclin complexes. Mouse p57 consists of four structurally distinct domains, a CDK inhibitory domain, a proline-rich domain, an a...

p57Kip2 and Cancer: Time for a Critical Appraisal

“…In human astrocytoma cell lines, p57 Kip2 accumulation reduced proliferation and induced a senescent phenotype (103). A similar p57 Kip2 -induced, senescence-like phenotype was observed in a PPC-1 prostate cancer cell line (104).…”

WISP3 is a novel tumor suppressor gene of inflammatory breast cancer

“…A detailed ultrastructural analysis by electron microscopy demonstrate that the WISP3 transfectants exhibited numerous cytoplasmic lysosomal bodies surrounded by a membrane, some containing electron-dense material and invaginated and convoluted nuclei (Figure 2b). These morphologic features have been described in cells undergoing senescence (Romanov et al, 2001;Tsugu et al, 2000).…”

Bcl-2 activates a programme of premature senescence in human carcinoma cells

“…In particular, activation of a senescence programme in neoplastic cells has been obtained either by reintroduction of critical regulators of replicative senescence [25,37] or by treatment with anti-cancer agents [42]. Most interestingly, expression of several CKI, in both normal and tumour cells [23,24], triggers premature senescence. Two molecular pathways appear to have a critical role in senescence in normal cells: the p16 INK4a /Rb pathway and the p53/p21 Cip1 pathway [43].…”

“…Cell lines derived from tumours are generally capable of extended proliferation: indeed, limitless replicative potential represents one of the de novo acquired capabilities of tumour cells, and the ability to repress senescence pathways appears to contribute to tumorigenesis [22]. Accordingly, restoration of senescence regulatory pathways in tumour cells rapidly elicits senescence [23][24][25]. These observations suggest that, in several immortal tumour-derived cell lines, the genetic programme of senescence is repressed, but not lost, in such a way that it can be reactivated by expression of critical regulators.…”