Silencing of Homeodomain-Interacting Protein Kinase 2 (HIPK2) Induces Anti-Adipogenic Effects in 3T3-L1 Adipocytes

Homeodomain-interacting protein kinase 2 (HIPK2) is an important regulator of various transcription factors and cofactors, which are involved in cell growth, cell death, and embryonic development. Previously, it has been reported that HIPK2 is upregulated during white fat development. However, the expression and functional role of HIPK2 during adipogenesis remain unclear. Here, we investigated the expression and biological function of HIPK2 during the adipogenesis of 3T3-L1 cells. Importantly, protein and mRNA expression of HIPK2 were significantly upregulated in a time-dependent manner during 3T3-L1 preadipocyte differentiation. Notably, distinct pharmacological inhibitors revealed the pivotal roles of p38 MAPK and PKC in the induction of HIPK2 expression during differentiation of 3T3-L1 cells. Moreover, knockdown of HIPK2 significantly reduced lipid storage and triglyceride (TG) levels without cytotoxicity during 3T3-L1 preadipocyte differentiation. At the mechanistic level, HIPK2 knockdown reduced the expression of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), perilipin A, leptin, and resistin, as well as the phosphorylation of signal transducer and activator of transcription-3 (STAT-3) during 3T3-L1 preadipocyte differentiation. Taken together, these results revealed that HIPK2 expression is significantly upregulated in p38 MAPK- and PKC-dependent manners, and this upregulation of HIPK2 plays a critical role in lipid accumulation during differentiation of 3T3-L1 cells, which is mediated by control of the expression and phosphorylation levels of C/EBP-α, PPAR-γ, STAT-3, FAS, and perilipin A.