Effects on the cell cycle may be mediated by interaction of Pura with cellular proteins including Cyclin/Cdk complexes and the Rb tumor suppressor protein.
The cyclin-dependent-kinase inhibitors (CDKN)/retinoblastoma (RB1) pathway has been implicated as having a role in medullary thyroid carcinoma (MTC) tumorigenesis.
Genes most commonly associated with the process of oncogenesis include: p53 inactivating mutation; hDM2 overexpression; p16 reduced expression; K-/H-RAS activating mutation; PTEN inactivating mutation/deletion; EGFR activating mutation and overexpression; retinoblastoma inactivating mutation and deletion; Cyclin proteins overexpression; CD95 reduced expression; protective BCL-2 proteins overexpression; to name but just a few of such molecules.
Combined, these results demonstrate that Shh/Gli2 signaling stimulates VSMC proliferation via regulation of the G(1) cyclin-retinoblastoma axis and suggest that antagonists that target the Shh pathway may be therapeutically beneficial in the prevention of intimal hyperplasia.
At the protein level, prolonged down-regulation of E2F-1 and proliferating cell nuclear antigen (PCNA), sustained expression of p21(WAF1/CIP1) and dephosphorylation of retinoblastoma (Rb) occurred in the sensitive cells.
Specifically, p16ink4a disrupts prereplication complex assembly by inhibiting mini-chromosome maintenance (MCM) protein loading in G1, while RB was found to disrupt replication in S phase through attenuation of PCNA function.
Retinas in C57Bl6 mice at embryonic day (E) 14, postnatal day (P) 1 and P11 were analyzed using immunohistochemistry with anti-p27(KIP1), threonine-187-phosphorylated p27(KIP1) (T187-phospho-p27), bromodeoxyuridine (BrdU), proliferating cell nuclear antigen (PCNA) antibodies, and phosphorylated histon H3 (pHiston H3), which is a marker for cells in M phase. p27(KIP1) knockout (-/-) mice and human retinoblastoma were also analyzed.
Immunohistochemical staining for various glial and neuronal markers, proliferative markers (MIB-1, Topoisomerase II alpha PCNA) and tumour suppressor gene protein expression of p53 and retinoblastoma (Rb) were performed.
Our results indicate that RXL motif-based inhibitors will provide selective antiproliferative agents with in vivo efficacy in tumors with deregulated Rb/cyclin D pathways.
Loss of p16INK4a expression would disrupt the retinoblastoma (Rb)/p16INK4a/cyclin D-dependent kinase (CDK4) pathway, whereas loss of p14ARF expression would inactivate both the Rb and p53/ MDM2/p14ARF pathways through MDM2, which can complex with either Rb or p53.