Comparative analyses of MYBL1 knockdown in non-tumor and triple negative breast cancer
cells
PROJECT SUMMARY
The MYBL1 gene belongs to the MYB family of genes, which includes c-MYB and MYBL2. The genes
are proto-oncogenes that function as strong transcriptional activators involved in proliferation,
differentiation and cell cycle signaling processes, all which are key events in tumor progression. Studies
showed that truncated c-MYB is an oncogene and as such, the gene was studied as a therapeutic target for
breast cancers. Less is known about MYBL1 and MYBL2. Both play substantial roles in cell cycle
progression and are overexpressed in different cancers, including breast cancers. Published results from
the Player laboratory showed MYBL1 overexpressed in a subpopulation of triple negative breast cancers
(TNBC). In a separate comprehensive supervised network analyses of luminal breast cancers, MYBL1
overexpression was shown to correlate with poor disease prognosis. Based on these studies the principal
investigator‘s (PI) laboratory chose to study the MYBL1 gene with an interest in characterizing the gene
in non-tumor TN compared to TNBC and identifying genes affected by its expression in the cancers. The
experimental approach is to knockdown the MYBL1 gene in the samples, perform microarray analyses to
identify genes differentially affected by the processes, followed by further analyses to authenticate
candidate genes identified during the process. As a proof of concept, MYBL1 gene was down-regulated
in a TNBC cell line. The candidate genes affected by decreasing MYBL1 expression include MYBL2 and
an enrichment in cell cycle signaling genes some of which are novel. This observation is consistent with
those which show co-expression of MYBL1 and MYBL2 and substantiate the ability of MYBL1 to
regulate expression of MYBL2. The experiments outlined in the current study should broaden our
understanding of signaling events in triple negative breast samples. For Aim 1, the investigators will
continue knockdown studies of MYBL1 in TNBC and include an additional TNBC and a non-tumor TN
sample as comparisons. These data will allow the PI to identify differential patterns of regulation by
MYBL1 in non-tumor compared to triple negative cancers in efforts to identify genes and processes that
might be associated with tumor progression. Because TNBC are heterogeneous, this study is confined to
subtype B, MYBL1 expressing samples. Reliable signature genes will be identified, and pathway analyses
performed. The hypothesis is that expression of MYBL1 in the different tissues result in different
signaling mechanisms. Select differentially expressed genes will be examined using tissue microarrays
with defined receptor status and survival data and compared to the MYBL1 gene expression pattern. For
Aim 2, the proliferative capacity and invasive potential of the various knockdown samples will be
compared. For Aim 3 the tumorigenic properties of control untreated, shRNA scrambled control and
MYBL1 shRNA knockdown preparations for each cell line will be examined via Soft Agar analyses.