PKA, PKC, and the protein phosphatase 2A influence HAND factor function: a mechanism for tissue-specific transcriptional regulation.

Wells Center for Pediatric Research, James Whitcomb Riley Hospital for Children, 702 Barnhill Drive, Room 2666, Indianapolis, IN 46202, USA.
Molecular Cell (Impact Factor: 14.02). 12/2003; 12(5):1225-37.
Source: PubMed


The bHLH factors HAND1 and HAND2 are required for heart, vascular, neuronal, limb, and extraembryonic development. Unlike most bHLH proteins, HAND factors exhibit promiscuous dimerization properties. We report that phosphorylation/dephosphorylation via PKA, PKC, and a specific heterotrimeric protein phosphatase 2A (PP2A) modulates HAND function. The PP2A targeting-subunit B56delta specifically interacts with HAND1 and -2, but not other bHLH proteins. PKA and PKC phosphorylate HAND proteins in vivo, and only B56delta-containing PP2A complexes reduce levels of HAND1 phosphorylation. During RCHOI trophoblast stem cell differentiation, B56delta expression is downregulated and HAND1 phosphorylation increases. Mutations in phosphorylated residues result in altered HAND1 dimerization and biological function. Taken together, these results suggest that site-specific phosphorylation regulates HAND factor functional specificity.

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Available from: Anthony B Firulli, Jul 25, 2014
    • "Implicated in the structural organisation during embryogenesis. Increases the phosphorylation of Hand1 (Firulli et al. 2003), which when activated is able to inhibit NANOG expression in the inner cell mass DNHD1 Dynein heavy chain domain 1-like: microtubule based movement DCN Decorin: Proteoglycan that interacts with collagen fibrils. Also a potent transforming growth factor b antagonist shown to regulate progenitor cell differentiation (Fetting et al. 2014). "

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    • "Dimer choice is regulated, in part, by a threonine and serine pair that is evolutionarily conserved among all Twist family members. Mimicking Hand1 hypophosphorylation through mutations in residues T107 and S109 enhances homodimer formation, whereas mimicking Hand1 phosphorylation at T107 and S109 enhances formation of E-protein heterodimers (Firulli et al., 2003). Indeed, changes in bHLH dimer choices affect craniofacial development (Connerney et al., 2006). "
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    ABSTRACT: In this study we examine the consequences of altering Hand1 phosphoregulation in the developing neural crest cells (NCCs) of mice. Whereas Hand1 deletion in NCCs reveals a nonessential role for Hand1 in craniofacial development and embryonic survival, altering Hand1 phosphoregulation, and consequently Hand1 dimerization affinities, in NCCs results in severe mid-facial clefting and neonatal death. Hand1 phosphorylation mutants exhibit a non-cell-autonomous increase in pharyngeal arch cell death accompanied by alterations in Fgf8 and Shh pathway expression. Together, our data indicate that the extreme distal pharyngeal arch expression domain of Hand1 defines a novel bHLH-dependent activity, and that disruption of established Hand1 dimer phosphoregulation within this domain disrupts normal craniofacial patterning.
    Full-text · Article · Aug 2014 · Development
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    • "RESEARCH ARTICLE Development (2014) 141, 1-11 doi:10.1242/dev.106336 DEVELOPMENT expressed by this transgene features substitution of the residues T103 and S105 with alanines (supplementary material Fig. S1), thereby preventing their phosphorylation; extrapolating from prior studies of Hand1 and Twist1, these changes may promote affinity for homodimerization rather than heterodimerization with E proteins (Firulli et al., 2003, 2005). We compared the effects of inducing expression of hand2, hand2 AA and hand2 P , using inducible transgenes to overexpress each variant (supplementary material Fig. S3). "
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    ABSTRACT: Embryonic heart formation requires the production of an appropriate number of cardiomyocytes; likewise, cardiac regeneration following injury relies upon the recovery of lost cardiomyocytes. The basic helix-loop-helix (bHLH) transcription factor Hand2 has been implicated in promoting cardiomyocyte formation. It is unclear, however, whether Hand2 plays an instructive or permissive role during this process. Here, we find that overexpression of hand2 in the early zebrafish embryo is able to enhance cardiomyocyte production, resulting in an enlarged heart with a striking increase in the size of the outflow tract. Our evidence indicates that these increases are dependent on the interactions of Hand2 in multimeric complexes and are independent of direct DNA binding by Hand2. Proliferation assays reveal that hand2 can impact cardiomyocyte production by promoting division of late-differentiating cardiac progenitors within the second heart field. Additionally, our data suggest that hand2 can influence cardiomyocyte production by altering the patterning of the anterior lateral plate mesoderm, potentially favoring formation of the first heart field at the expense of hematopoietic and vascular lineages. The potency of hand2 during embryonic cardiogenesis suggested that hand2 could also impact cardiac regeneration in adult zebrafish; indeed, we find that overexpression of hand2 can augment the regenerative proliferation of cardiomyocytes in response to injury. Together, our studies demonstrate that hand2 can drive cardiomyocyte production in multiple contexts and through multiple mechanisms. These results contribute to our understanding of the potential origins of congenital heart disease and inform future strategies in regenerative medicine.
    Full-text · Article · Jul 2014 · Development
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