Regulation of calpain 2 expression by miR-223 and miR-145.

Calpain 2 (CAPN2) is a Ca²⁺-dependent cysteine-protease that is involved in different cellular processes. Despite its important role, little is known about how CAPN2 expression is regulated. This study addressed the potential regulation of CAPN2 by microRNAs (miRNAs) in human endothelial cells. Two miRNAs were found to regulate CAPN2 expression by two distinct mechanisms, one direct and the other indirect. MiR-223 directly targeted CAPN2 by binding to the CAPN2 3'-untranslated region. Mir-223 overexpression decreased CAPN2 protein levels in cultured cells and in mice miR-223 antagonism led to an increase in CAPN2 protein in lung tissue. MiR-145 overexpression also decreased CAPN2 expression but did not affect a CAPN2 luciferase construct, indicating that the effect was indirect. MiR-145 targets histone deacetylase (HDAC) 2, and HDAC inhibition transcriptionally regulated CAPN2 expression by hyperacetylation of the promoter of CAPN2 gene and a subsequent decrease in polymerase 2 binding. Indeed, down regulation of HDAC2 by miR-145 not only decreased CAPN2 protein expression and calpain activity, but also protected paxillin against calpain-dependent degradation. Thus, protein levels of CAPN2 are regulated by miR-223, acting directly on the 3'-untranslated region as well as by miR-145, which acts via an increase in HDAC2. ENZYMES: Calpain 2 (EC 3.4.22.53), histone deacetylase 2 (EC 3.5.1.98).

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