BMP-SMAD1/4 upregulates HNF4α in a subset of heterogeneous mouse pancreatic cancer cells while under metabolic stress
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Date
29/11/2013Author
Heung, Man Yeung
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Abstract
It is not known whether pancreatic cancers evolve from a single or multiple cells, or
from a particular pancreatic lineage. However, in the Pdx1-Cre; LSL-KrasG12D; LSLTp53R172H
mouse model of pancreatic cancer, all pancreatic lineages are susceptible
to express mutant KRas and p53. Hence, such mouse model implies a scenario of
maximal heterogeneity of cancer cell origins. On this basis, I isolated seven subclones
of heterogeneous mouse pancreatic cancer cells from a single tumour; each of
them had a distinct morphology and gene expression profile. Notably, they
possessed different intrinsic phospho-SMADs downstream of the TGFβ receptor
(phospho-SMAD2/3) or the BMP receptor (Phospho-SMAD1/5/8). I discovered that
SMAD4, a co-SMAD which is frequently found to be lost in pancreatic caner tissues,
upregulated HNF4α via the classical BMP-SMAD1 pathway, when cells were
experiencing metabolic stress upon deprivation of serum, or in the presence of excess
thymidine. Under serum starvation at a hypoglycemic-like glucose concentration, the
HNF4α-expressing sub-clones appeared to be more able to sustain an unstressed
morphology than other non-HNF4α-expressing sub-clones. Immunohistochemical
staining on pancreatic cancer sections revealed nuclear co-localization of SMAD4
and HNF4α in human (half of the cases) and in mouse samples. As a secondary
project conducted during characterization of cells, I also found that three of the subclones
more robustly proliferated under anchorage independent conditions, and they
relied on the MEK-ERK pathway and the canonical Wnt pathway, to a different
degree. Both studies demonstrate for the first time in primary cell culture that
pancreatic cancer cells within a tumour could be highly heterogeneous in terms of
both morphology and signaling pathways.