The muscle ankyrin repeat proteins: CARP, ankrd2/Arpp and DARP as a family of titin filament-based stress response molecules.

ankrd-2/Arpp, and are three members of a conserved gene family, referred to here as (muscle ankyrin repeat proteins). The expression of Mduanyu37s is induced upon injury and hypertrophy stretch or denervation (ankrd2/Arpp), and during recovery following starvation suggesting that they are involved in muscle stress response pathways. Here, we show that family members contain within their ankyrin repeat region a binding site for the myofibrillar elastic protein titin. Within the myofibril, myopalladin, and the calpain protease p94 appear to be components of a titin N2A-based signaling complex. Ultrastructural studies demonstrated that all three endogenous Mduanyu37 proteins co-localize with I-band titin N2A epitopes in adult heart muscle tissues. In cultured fetal rat cardiac myocytes, passive stretch induced differential distribution patterns of and staining for both proteins was increased in the nucleus and at the I-band region of myofibrils, while staining also increased at intercalated discs. We speculate that the myofibrillar Mduanyu37s are regulated by stretch, and that this links titin-N2A-based myofibrillar stress/strain signals to a regulation of muscle gene expression.

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