Cytosolic dynamics of annexin A6 triggers feedback regulation of hypertrophy via atrial natriuretic peptide in cardiomyocytes [Signal Transduction]
January 8th, 2014 by Banerjee, P., Bandyopadhyay, A.
Malfunctions in regulatory pathways that control cell size are prominent in pathological cardiac hypertrophy. Here, we show annexin A6 (Anxa6) to be a crucial regulator of atrial natriuretic peptide (ANP) mediated counter-hypertrophic responses in cardiomyocytes. Adrenergic stimulation of H9c2 cardiomyocytes by phenylephrine (PE) increased the cell size with enhanced expression of biochemical markers of hypertrophy, concomitant with elevated expression and subcellular redistribution of Anxa6. Stable cell lines with controlled increase in Anxa6 levels were protected against PE induced adverse changes whereas Anxa6 knockdown augmented the hypertrophic responses. Strikingly, Anxa6 knockdown also abrogated PE-induced juxta- nuclear accumulation of secretory granules (SG) containing ANP propeptides (proANP), a signature of maladaptive hypertrophy having counteractive functions. Mechanistically, PE treatment prompted a progressive and dynamic association of Anxa6 with proANP- SG, parallel to their participation in anterograde traffic, in an isoform-specific fashion. Moreover, Anxa6 mutants that failed to associate with proANP hindered ANP- mediated protection against hypertrophy, which was rescued, at least partially, by WT Anxa6. Additionally, elevated intracellular calcium (Ca2+) stimulated Anxa6-proANP colocalization and membrane association. It also rescued proANP translocation in cells expressing an Anxa6 mutant (Anxa6ΔC). Furthermore, stable overexpression of Anxa6T356D, a mutant with superior flexibility, provided enhanced protection against PE, compared to WT, presumably due to enhanced membrane-binding capacity. Together, present study delivers a cooperative mechanism where Anxa6 potentiates ANP dependent counter-hypertrophic responses in cardiomyocytes by facilitating regulated traffic of proANP.