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  4. Ca2+ Channel Independent Functions Of An Alternatively Spliced ß4 Subunit

Ca2+ Channel Independent Functions Of An Alternatively Spliced ß4 Subunit

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yl682.pdf (3.75 MB)
Permanent Link(s)
https://hdl.handle.net/1813/38955
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Cornell Theses and Dissertations
Author
Lee, Yoon Jung
Abstract

The [beta] subunits of voltage-gated Ca2+ channels are multifunctional proteins, which act primarily as a Ca2+ channel regulatory subunit to regulate trafficking and gating properties of pore-forming Ca2+ channel [alpha]1 subunits. Recent studies have revealed, however, that [beta]4 subunits also play crucial roles in a variety of Ca2+ channel independent functions. These processes involve translocation of [beta] subunits to the nucleus where they associate with and regulate expression of proteins involved in gene transcription. The latter emerging role of the Ca2+ channel [beta]4 subunit began with the cloning of various alternatively spliced isoforms of the [beta]4 subunit. Here we cloned the mammalian form of an alternatively spliced, truncated [beta]4 subunit ([beta]4c-207aa) from human brain, and showed that it interacts with heterochromatin protein 1[gamma] (HP1[gamma]) through a PXVXL consensus motif. We also showed that [beta]4c is highly expressed in vestibular, and deep cerebellar nuclei of mouse brain. In our subsequent study, we found that [beta]4c nuclear transport is independent of its PXVXL motif interaction with HP1[gamma]. Instead, we found that the nuclear targeting of heterologously expressed [beta]4c in Neuro2a cells is under the control of two sequence motifs that are separated by 63 amino acids. The first is identical to a classical monopartite nuclear localization sequence (cNLS), K(K/R)X(K/R), located in the HOOK domain, and the second is a previously unidentified C-terminal sequence that is generated by alternative splicing. Both sequences are required for optimal targeting of [beta]4c to the nucleus. Next we determined the functional consequences of [beta]4c nuclear targeting by performing a whole genome expression study. We determined that [beta]4c regulates the transcription of a number of genes that include components of the cytoskeleton assembly machinery and other ion channel genes. Notably, [beta]4c did not regulate expression of Ca2+ channel genes. The [beta]4c splice variant was not capable of modulating Ca2+ channel trafficking or gating properties. Therefore, the overall conclusion of this thesis is that [beta]4c does not affect the expression or function of Ca2+ channel subunits, rather it acts independently of Ca2+ channels to regulate genes that are involved in neurite outgrowth.

Date Issued
2014-08-18
Committee Chair
Horne, William Alan
Committee Member
Oswald, Robert Edward
Lin, David M.
Weiss, Robert S.
Degree Discipline
Physiology
Degree Name
Ph. D., Physiology
Degree Level
Doctor of Philosophy
Type
dissertation or thesis

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