Abstract

UbcH5c, a member of the UbcH5 family of protein ubiquitin conjugase E2 enzymes, is a critical component of biological processes in human cells, being the initial ubiquitinating enzyme of substrates like IκB, TP53, and cyclin D1. We report here that the metastasis regulator protein SLUG inhibits the expression of UbcH5c directly through chromatin remodeling and thus, among other downstream effects, elevates the level of cyclin D1, thus enhancing the growth rates of breast cancer cells. Overexpression of SLUG in the SLUG-deficient breast cancer cells significantly decreased the levels of mRNA and protein of UbcH5c but only elevated the protein levels of cyclin D1. On the contrary, knockdown of SLUG in SLUG-high breast cancer cells elevated the levels of UbcH5c while decreasing the level of cyclin D1 protein. SLUG is recruited at the E2-box sequence at the UbcH5c gene promoter along with the corepressor CtBP1 and the effector HDAC1 to silence the expression of this gene. Knockdown of UbcH5c in the SLUG-deficient human breast cells elevated the level of cyclin D1 as well as the rates of proliferation and invasiveness of these cells. Whereas the growth rates of the cells are enhanced due to overexpression of SLUG or knockdown of UbcH5c in the breast cancer cells tested, ER(+) cells also acquire resistance to the anti-estrogen 4-hydroxytamoxifen due to the rise of cyclin D1 levels in these cells. This study thus implicates high levels of SLUG and low levels of UbcH5c as a determinant in the progression of metastatic breast cancer.

Highlights

  • Chains, with ubiquitin moieties connected through isopeptide linkage between the ⑀-amide group of lysine and the carboxyl end of glycine, is the critical prerequisite of proteasomal degradation of proteins [4]

  • Because cyclin D1 levels in the cells may determine these properties, we initially evaluated whether there is a correlation between the levels of SLUG and cyclin D1 in different human breast cancer tissues and cells

  • Several interdependent and independent mechanisms may lead to the elevation of cyclin D1 levels in breast cancer cells

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Summary

Introduction

Chains, with ubiquitin moieties connected through isopeptide linkage between the ⑀-amide group of lysine and the carboxyl end of glycine, is the critical prerequisite of proteasomal degradation of proteins [4]. C, evaluation of SLUG, cyclin D1, and UbcH5c protein levels in four different breast cancer cell lines by Western blotting. To evaluate whether SLUG expression has direct correlation with increased cyclin D1 levels in the breast cells, we overexpressed SLUG in SLUG-negative MDA-MB-468 and MCF7 cells [33] and generated multiple SLUG-transfected populations and respective vector-transfected controls.

Results
Conclusion
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