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Functional analysis of Hic-5/ARA55 isoforms in C2C12 myogenesis

by Gao, Zhengliang

Abstract (Summary)
Hic-5 is a focal adhesion protein of paxillin superfamily that was initially cloned from mouse osteoblasts as a TGF-�² or H2 O2 inducible cDNA. As well, Hic-5 was independently identified as an Androgen receptor activator (ARA55). Conflicting data have implicated Hic-5 in opposing processes. With two Hic-5 isoforms documented, I hypothesized that multiple Hic-5 isoforms may exist that have both overlapping and isoform-specific functions, which may explain those discrepancies. To test this hypothesis, I have utilized C2 C12 myoblasts and analyzed the roles of Hic-5 isoforms in development and homeostasis. 1 . I have confirmed the presence of the two previous reported Hic-5 isoforms (�± and �²) and uncovered 10 additional novel Hic-5 transcripts. Conceptually translated proteins from these transcripts significantly differ at the N-terminal region and likely have distinct binding properties and functions. Hic-5 isoforms have distinct tissue distribution and are developmentally regulated in the mouse mammary gland in vivo (Chapter two ). 2 . I found that: (a)� myoblasts express multiple Hic-5 isoforms; (b)� the two predominant isoforms, Hic-5�± and Hic-5�², are differentially expressed during myogenesis; (c)� any experimentally-induced change in Hic-5 expression results in a substantial increase in apoptosis during differentiation; (d)� ectopic expression of Hic-5�± is permissive to differentiation while expression of either Hic-5�² or antisense Hic-5 reduces myoblast chemo-differentiation and blocks fusion; (e)� Hic-5 localizes to focal adhesion in C2C12 myoblasts and perturbation of Hic-5 leads to defects in cell spreading; (f)� perturbations of Hic-5 expression interfere with the normal expression dynamics of laminin; and (g)� the rescue of myoblast survival and differentiation by laminin but not fibronectin suggests that Hic-5 isoforms differentially regulate myogenesis due to their different impacts on cell-ECM interaction, focal adhesion dynamics and integrin signaling ( Chapter Three ). In summary, the roles Hic-5 may assume in development and homeostasis are complex and the different Hic-5 isoforms may mediate distinct physiological and/or pathological responses in cells. Therefore, a more precise analysis of Hic-5 isoforms is required to more fully understand the roles of not only Hic-5, but also integrin signaling in normal and diseased cells ( Chapter four and five ).
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Advisor:

School:University of Massachusetts Amherst

School Location:USA - Massachusetts

Source Type:Master's Thesis

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Date of Publication:01/01/2006

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