Oral Presentation 6th Australian Health and Medical Research Congress 2012

The mammalian intestinal epithelium has a remarkable capacity to regenerate following injury such as DNA damage or surgical resection.  To determine the role of gp130/Stat3 during intestinal regeneration we irradiated mutant mice with hyperactive or reduced gp130/Stat3 signaling.  We observed increased regeneration in gp130^F/F mice (the F/F mutation prevents Socs3 mediated repression of the gp130 receptor) which have hyperactive gp130/Stat3 signaling, and conversely, inhibition of gp130/Stat3 signaling reduced intestinal regeneration. We have previously demonstrated a critical role for Wnt signaling during regeneration and observed that Wnt is intact and active in the non-regenerating crypts of Stat3^+/- mice.  This suggests that Wnt signaling alone is insufficient to promote regeneration and that gp130/Sta3 signaling is also required.  To confirm these findings in a non-DNA damage model we utalised organoid cultures.  Organoids from gp130^F/F mice grew significantly more crypts per organoid and conversely inhibition of Stat3 reduced crypt formation demonstrating a cell autonomous role for gp130/Stat3 during intestinal regeneration.

We next asked if gp130/Stat3 could therefore regulate Wnt induced intestinal tumourigenesis. Apc^Min/+;gp130^F/Fdisplayed a significantly reduced lifespan associated with an increase in intestinal tumor number and size.  Conversely, inhibition of gp130/Stat3 significantly reduced Wnt induced intestinal tumourigenesis and tumor growth, even in the presence of nuclear β-catenin.  These findings were confirmed in human SW480 colon cancer cells during colony forming assays and xenografts.  Mechanistically we identified the polycomb repressor Bmi-1 as a direct Stat3 target and thus, down regulation of Bmi-1 when gp130/Stat3 was inhibited resulted in increased expression of cell-cycle arrest genes p16 and p21.  This was functionally demonstrated in Apc^Min/+;Bmi-1^+/- mice which developed smaller intestinal tumors which expressed high p16 and p21.  These data establish a novel role for gp130/Stat3 signaling which enables manipulation of this pathway to be exploited in regenerative medicine and targeted therapeutically for the treatment of cancers with deregulated Wnt signaling, even if gp130/Stat3 itself is not mutated.