Promotes dimerization of NF-kappa-B subunits and regulates NF-kappa-B transcription factor activity (By similarity). Plays a role in the regulation of the growth of actin filaments. Inhibits the activity of the F-actin-capping protein complex formed by the CAPZA1 and CAPZB heterodimer. Promotes growth of cardiomyocytes, but not cardiomyocyte proliferation. Promotes cardiac muscle hypertrophy. {ECO:0000250, ECO:0000269|PubMed:10329199, ECO:0000269|PubMed:16895918, ECO:0000269|PubMed:20625546}. This is the function of MTPN (myotrophin, ENSG00000105887).