MmuEX0044725 @ mm9

Several forms of alphaII-spectrin (SPTAN1) are expressed in heart, including one, termed alphaII-SH3i, which contains a 20-amino acid sequence next to the SH3 domain of repeat 10 (MmuEX0044725). In adult mouse heart, antibodies to all forms of alphaII-spectrin labeled the sarcolemma, transverse (?t-?) tubules and intercalated disks of cardiomyocytes. In contrast, antibodies specific for alphaII-SH3i labeled only gap junctions and transverse tubules. In transgenic hearts, in which the JNK pathway was constitutively activated, alphaII-SH3i was lost specifically from gap junctions but not from t-tubules while other isoforms of alphaII-spectrin were retained at intercalated disks. Immunoprecipitations confirmed the decreased association of alphaII-SH3i with connexin 43 (Cx43) in transgenic hearts compared to controls. Furthermore, activation of JNK in neonatal myocytes blocked the formation of gap junctions by exogenously expressed Cx43-GFP fusion protein. Similarly, over-expression of the SH3i fragment in the context of repeats 9-11 of alphaII?spectrin specifically caused the accumulation of Cx43-GFP in the perinuclear region and inhibited its accumulation at gap junctions. These results support a critical role for the alphaII-SH3i isoform of spectrin in intracellular targeting of Cx43 to gap junctions and implicates alphaII-SH3i as a potential target for stress signaling pathways that modulate intercellular communication.