Graduation Year

2007

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Cancer Biology

Keywords

Mitosis, Transcription, Mcl-1, Rb

Abstract

One of the main results of Rb-E2F pathway disruption is deregulation of the E2F family of transcription factors, which can lead to inappropriate proliferation, oncogenic transformation, or the induction of apoptosis. Given the potential negative biological effects associated with deregulated E2F activity, it is of great importance to study E2F targets that mediate these effects. In Part I of this manuscript, we identify the RhoBTB2 putative tumor suppressor gene as a direct physiological target of the E2F1 transcription factor. We find that RhoBTB2 is highly upregulated during mitosis due in part to E2F1, and that overexpression of RhoBTB2 increases the S-phase fraction and slows the rate of proliferation. We also find RhoBTB2 similarly upregulated during drug-induced apoptosis due primarily to E2F1 and that knockdown of RhoBTB2 expression via siRNA slows drug-induced apoptosis.

Taken together, we describe RhoBTB2 as a novel direct target of E2F1 with roles in cell cycle and apoptosis. In Part II, we independently identify from cancer cell lines two novel variants from the promoter of E2F1 target MCL-1---MCL-1 +6 and +18---as initially published by Moshynska et al (1). In contrast to Moshynska et al., we find the variant promoters identically present in both cancerous and adjacent noncancerous clinical lung samples, suggesting that the variants are germ-line encoded. We also find the variant promoters prevalent in genomic DNA derived from healthy control samples and present at frequencies similar to that observed in cancerous cell lines. In further contrast, we find the activity of the MCL-1 +6 and +18 promoters approximately 50% less than the common MCL-1 +0 promoter---both during normal cellular homeostasis and under conditions that actively induce Mcl-1 transcription.

Given our results and those of others, we conclude that the MCL-1 +6 and +18 promoters are likely benign polymorphisms and do no [sic] represent a reliable prognostic marker for CLL as reported by Moshynska et al.

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