Temperature-dependent Modification and Activation of B-MYB: IMPLICATIONS FOR CELL SURVIVAL

Giorgia Santilli,Rebekka Schwab,Roger Watson,Cathy Ebert,Bruce J Aronow,Arturo Sala

doi:10.1074/jbc.m411747200

Abstract

B-MYB is a ubiquitous transcription factor with an essential role in mouse development. Because cells with a disrupted B-MYB gene cannot be obtained, it is still unknown what is the critical function(s) exerted by B-MYB in mammalian cells. In this study we have observed that reducing B-MYB expression in primary human fibroblasts by using RNA interference results in a partial block of the cells in the G(2) phase of the cell cycle and cell death. Surprisingly, suppressing B-MYB transcriptional activity with a dominant-negative molecule is without effect, suggesting that its transactivating function is not essential. Only human or murine fibroblasts exposed to high temperature are sensitized to cell death in the presence of dominant-negative B-MYB. This correlates with temperature-dependent binding of endogenous B-MYB to transcriptional regulatory elements of the stress-related gene ApoJ/clusterin. We find that regulation of ApoJ/clusterin by B-MYB is a pro-survival response to thermal stress. Thus, B-MYB is regulated by temperature to activate genes required for cell survival.

Highlights

B-MYB is a ubiquitous transcription factor with an essential role in mouse development
It is homologous to the prototype member of the MYB family, the protooncogene c-MYB, which is prevalently expressed in hematopoietic cells where it controls their differentiation and proliferation [2]
In our laboratory we have found no evidence of c-MYB, A-MYB, or B-MYB activation in DNA-damaged neuronal cancer cell lines suggesting that more studies are needed to fully understand the role of MYB genes in neuron demise [20]

Summary

Introduction

B-MYB is a ubiquitous transcription factor with an essential role in mouse development. Human or murine fibroblasts exposed to high temperature are sensitized to cell death in the presence of dominant-negative B-MYB This correlates with temperature-dependent binding of endogenous B-MYB to transcriptional regulatory elements of the stress-related gene ApoJ/clusterin. All MYB family members bind to the same consensus sequence (C/T)AACNG in in vitro assays, reflecting their high homology in the DNA-binding domain region [2] It is possible, that the different MYB proteins regulate different genes in vivo after post-translational modifications or interaction with specific cofactors [3, 4]. B-MYB has been shown to bind to and suppress the cyclin-dependent kinase inhibitor p57kip2 [30] These studies unveil a high level of complexity of B-MYB functions and support a model in which B-MYB regulates cell homeostasis by modulating both gene transcription and the activity of other. The absence of viable mouse embryonic cells with a disrupted BMYB gene has hampered more rigorous studies of its functions in vivo

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Conclusion