Targeted Disruption of the Murine Homeodomain-Interacting Protein Kinase-2 Causes Growth Deficiency In Vivo and Cell Cycle Arrest In Vitro

Abstract

The homeodomain-interacting protein kinase 2 (HIPK2) protein is a member of a recently identified family of nuclear protein kinases that are well conserved in various organisms. HIPK2 can bind to several homeotic factors and to a series of proteins involved in the regulation of cell survival and proliferation in response to morphogenetic and genotoxic signals. Here we report Hipk2-targeted disruption in mouse; Hipk2(-/-) mice are viable and fertile but significantly smaller than their wild-type littermates. This feature is present at birth and retained throughout the mouse adulthood. Mouse embryo fibroblasts from Hipk2(-/-) mice show a reduced proliferation rate, compared to the wild-type counterparts, with accumulation in the G0/G1 phase of the cell cycle and altered levels of the cell cycle regulators cyclin D and CDK6. Restoration of wild-type HIPK2 expression in Hipk2(-/-) cells rescues the normal phenotype supporting a role for HIPK2 in the regulation of cell proliferation.

Homeodomain-interacting protein kinase 2 plays an important role in normal terminal erythroid differentiation

“…These findings are consistent with other studies implicating the role of Hipk2 in regulation of cell survival and proliferation 7,11,14,18,22 but are the first involving erythropoiesis specifically.…”

“…Mice deficient in either Hipk1 or Hipk2 alone were initially reported to be grossly normal and fertile, 5,6 but a more recent study has shown that Hipk2 Ϫ/Ϫ mice are significantly smaller than their wild-type littermates through adulthood but show no difference in hematology, blood chemistry, or pathology. 7 Studies on the Hipk2 Ϫ/Ϫ mouse have also implicated HIPK2 in the regulation of cell proliferation and apoptosis. Survival and proliferation defects were observed in single neurons in the Hipk2 knockout, 5 and mouse embryonic fibroblasts from these mice also showed reduced proliferation with accumulation in the G 0 /G 1 phase of the cell cycle.…”

“…Survival and proliferation defects were observed in single neurons in the Hipk2 knockout, 5 and mouse embryonic fibroblasts from these mice also showed reduced proliferation with accumulation in the G 0 /G 1 phase of the cell cycle. 7 HIPK2 also binds several regulators involved in cell survival: the tumor suppressor p53, [8][9][10] antiapoptotic transcription factors Brn3a 5 and CtBP, 11 as well as the oncogenes c-Myb 12 and c-Ski 13 ; Hipk2 is also required for TGF␤-dependent survival of murine dopaminergic neurons 14 and helps to regulate the G 1 /S transition in epidermal cells through interactions with ␤-catenin and CtBP. 15 Many other binding partners of HIPK2 play significant roles in the regulation of hematopoietic differentiation, including Smad1-4, p300, AML1, MOZ, Groucho, HDAC1, c-Myb, c-Jun, c-Fos, and Pax6 2,4,12,16,17 ; knockdown of HIPK2 in hematopoietic cell lines recently uncovered a role for Hipk2 in cell-cycle arrest during non-DNA damage conditions, such as terminal differentiation and growth factor deprivation.…”

Homeodomain-interacting Protein Kinase-2 Stabilizes p27kip1 by Its Phosphorylation at Serine 10 and Contributes to Cell Motility

“…5A). As already reported for other cell types (10,11), HIPK2 depletion reduced the proliferation rate of H1299 cells as shown by the reduced cell number of H1299i compared with H1299-CV control cells and by the mild increase of the G 1 phase of the cell cycle (supplemental Fig. S2).…”

“…On the other hand, by phosphorylating the antiapoptotic corepressor C-terminal binding protein (CtBP) at serine 422, HIPK2 targets CtBP for proteasomal degradation and induces apoptosis even in p53-null cells (9). These events contribute to the cell response to UV, ionizing irradiation and several anticancer drugs and are impaired in HIPK2-depleted cells (10,11), suggesting a role for HIPK2 as a tumor suppressor. Indeed, there are examples of HIPK2 inactivation in human cancers such as HIPK2 mutations in cases of acute myeloid leukemia (12) or HIPK2 cytoplasmic mislocalization in breast carcinomas and in leukemogenesis (13,14).…”