| First Author | Jirawatnotai S | Year | 2004 |
| Journal | J Biol Chem | Volume | 279 |
| Issue | 49 | Pages | 51100-6 |
| PubMed ID | 15456744 | Mgi Jnum | J:95201 |
| Mgi Id | MGI:3525436 | Doi | 10.1074/jbc.M409080200 |
| Citation | Jirawatnotai S, et al. (2004) Cdk4 is indispensable for postnatal proliferation of the anterior pituitary. J Biol Chem 279(49):51100-6 |
| abstractText | For proper development and tissue homeostasis, cell cycle progression is controlled by multilayered mechanisms. Recent studies using knock-out mice have shown that animals can develop relatively normally with deficiency for each of the G1/S-regulatory proteins, D-type and E-type cyclins, cyclin-dependent kinase 4 (Cdk4), and Cdk2. Although Cdk4-null mice show no embryonic lethality, they exhibit specific endocrine phenotypes, i.e. dwarfism, infertility, and diabetes. Here we have demonstrated that Cdk4 plays an essential non-redundant role in postnatal proliferation of the anterior pituitary. Pituitaries from wild-type and Cdk4-null embryos at embryonic day 17.5 are morphologically indistinguishable with similar numbers of cells expressing a proliferating marker, Ki67, and cells expressing a differentiation marker, growth hormone. In contrast, anterior pituitaries of Cdk4-null mice at postnatal 8 weeks are extremely hypoplastic with markedly decreased numbers of Ki67+ cells, suggesting impaired cell proliferation. Pituitary hyperplasia induced by transgenic expression of human growth hormone-releasing hormone (GHRH) is significantly diminished in the Cdk4+/- genetic background and completely abrogated in the Cdk4-/- background. Small interfering RNA (siRNA)-mediated knockdown of Cdk4 inhibits GHRH-induced proliferation of GH3 somato/lactotroph cells with restored expression of GHRH receptors. Cdk4 siRNA also inhibits estrogen-dependent cell proliferation in GH3 cells and closely related GH4 cells. In contrast, Cdk6 siRNA does not diminish proliferation of these cells. Furthermore, Cdk4 siRNA does not affect GHRH-induced proliferation of mouse embryonic fibroblasts or estrogen-dependent proliferation of mammary carcinoma MCF-7 cells. Taken together, Cdk4 is dispensable for prenatal development of the pituitary or proliferation of other non-endocrine tissues but indispensable specifically for postnatal proliferation of somato/lactotrophs. |
