Absolute requirement for STAT3 function in small-intestine crypt stem cell survival

Abstract

The transcription factor signal transducer and activator of transcription 3 (STAT3) is frequently activated in human cancers. Interestingly, STAT3 also maintains the pluripotency and self-renewal of murine embryonic stem cells, and several tissue stem cell types. To investigate whether STAT3 also maintains the small-intestine crypt stem cell, we conditionally inactivated a Floxed Stat3 allele (Stat3 fl) in murine small-intestine crypt stem cells. Following Cre recombinase expression, apoptosis increased in Stat3 fl/ experimental crypts relative to Stat3 wt/ controls before declining. Control Stat3 wt/ mice carrying a Flox-STOP LacZ reporter transgene stably expressed LacZ after Cre induction. In contrast, Stat3 fl/ intestine LacZ expression initially increased modestly, before declining to background levels. Quantitative PCRs revealed a similar transient in recombined Stat3 fl allele levels. Long-term bromodeoxyuridine labelling directly demonstrated that functional STAT3 is required for 4 to 6 region label-retaining small-intestine stem cell survival. Rapid clearance of recombined Stat3 fl/ cells involves apoptosis potentially induced by elevated c-Myc in non-recombined cells and involves elevated p53 expression and caspase 3 activation. Intriguingly, Stat3 fl/ intestine recombination triggered dramatically upregulated polycomb transcriptional repressor Bmi1-potentially accelerating recombined crypt repopulation. In summary, STAT3 activity is absolutely required for small-intestine crypt stem cell survival at both the 4 to 6 label-retaining and crypt base columnar cell locations. © 2011 Macmillan Publishers Limited All rights reserved.