Of NuMA and chromatin: From the chromatin remodeling ISWI complex BWICH to the transcription factor LEDGF

Swaathi Jayaraman, Purdue University

Abstract

The primary function of the eukaryotic nucleus is to express the human genome. The organization of the nucleus, which is closely linked to the regulation of gene expression, is different between cell phenotypes and physiological states. The nuclear mitotic apparatus (NuMA) protein participates in mitotic spindle poles maintenance and stabilization. In the interphase nucleus, a function for NuMA in the nuclear organization and post-mitotic nuclear assembly are proposed. Recent work in Lelièvre laboratory has identified a novel role for NuMA in the control of chromatin organization in non-neoplastic mammary epithelial (S1) cells. NuMA interacts with the ISWI-family chromatin remodeling ATPase SNF2h leading to our hypothesis that the interaction between NuMA and chromatin associated proteins involved in the control of gene expression impacts cell homeostasis. In the present study, we found that NuMA interacts with four chromatin-associated proteins namely WSTF, NM1, Rsf1 and LEDGF in S1 cells. From these four NuMA-interacting partners, we chose the B-WICH complex (SNF2h, WSTF and NM1) and LEDGF as targets for further investigation. NuMA association with the B-WICH complex, which participates in ribosomal DNA (rDNA) transcription, led to the investigation of NuMA involvement in ribosome biogenesis. In this study, NuMA redistributes upon inhibition of rDNA transcription, present in the nuclear and cytoplasmic ribosome fractions, shows the presence of a putative RNA biding region and interacts with RNA polymerase I, 60S ribosomal subunit protein RPL26 and the ribosomal subunits nuclear export receptor Crm1. Silencing NuMA expression led to up-regulation of RPL26 expression. Furthermore, altering NuMA localization in living cells affected the movement of RPL26 from the nucleus to the cytoplasm. Collectively, these results indicate a novel involvement for NuMA in ribosome biogenesis, possibly linked to the nuclear transport of 60S ribosomal subunit. Investigation of LEDGF reveals drastic decrease in its expression upon progression of aggressive triple negative basal-like breast cancer from a preinvasive to an invasive stage in the HMT-3522 DCIS-like S2 and IDC-like T4-2 cancer progression cell culture models. This model also recapitulates the drastic loss of cancer stem cells observed in vivo during invasive progression. In S2 cells, LEDGF expression shows tendency towards lower expression with increase in tumor nodule size. Also, in S2 cells but not T4-2 cells, LEDGF and LEDGF regulated anti-oxidant protein 2 (AOP2) changed expression upon oxidative stress, which is important for triple negative breast cancer progression. Collectively these studies identified a novel involvement of LEDGF in the progression of TNBC, which requires further investigation. The different functions of NuMA in the context of gene expression regulation and thus, in the control of cell phenotypes are discussed. These functions collectively indicate that NuMA plays a major role in the overall control of gene expression, thus acting as a major contributor in maintaining cell homeostasis.

Degree

Ph.D.

Advisors

STAUFFACHER, Purdue University.

Subject Area

Biology|Cellular biology

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