Transcriptome of MEFs with BMP2 and DNA damage reagents

The tightly controlled BMP-Smad1 pathway is essential for embryonic development and postnatal tissue homeostasis. Dysfunction of BMP-Smad1 signaling also leads to tumor development such as juvenile polyposis and Cowden syndromes and various tumors in mouse models, with unknown pathological mechanisms. Here we establish a link between the BMP-Smad pathway and the prominent tumor suppressor Atm-p53 pathway. We identify activated nuclear Smad1 as an Atm substrate under genotoxic stress. Atm-mediated Smad1 S239 phosphorylation disrupts Smad1 interaction with protein phosphatase PPM1A and enhances Smad1 activation and up-regulation, which not only turns on target genes including Cdk1nc but also interacts with p53 and inhibits Mdm2-mediated p53 ubiquitination, leading to p53 stabilization. Functionally, Smad1 acts like a tumor suppressor in DNA damage response, cell transformation and tumorigenesis in a p53-dependent manner. Sequencing of the gastric cancer samples revealed that Smad1 is frequently mutated, with S239 as mutational hotspot. This study thus establishes the BMP-Smad1 pathway as an integral part of DNA damage response, which can suppresses tumorigenesis via p53. Transformed MEFs (Smad1f/f, Smad1f/f Cre) treated with 50ng/ml BMP2, 1 ug/ml doxorubincin, or both for different periods of time. The mRNA levels of all genes were compared using microarray analysis.