CTCF Expression is Essential for Somatic Cell Viability and Protection Against Cancer.

CCCTC-binding factor (CTCF) is a conserved transcription factor that performs diverse roles in transcriptional regulation and chromatin architecture. Cancer genome sequencing reveals diverse acquired mutations in , which we have shown functions as a tumour suppressor gene. While CTCF is essential for embryonic development, little is known of its absolute requirement in somatic cells and the consequences of haploinsufficiency. We examined the consequences of CTCF depletion in immortalised human and mouse cells using shRNA knockdown and CRISPR/Cas9 genome editing as well as examined the growth and development of heterozygous () mice. We also analysed the impact of haploinsufficiency by examining gene expression changes in -altered endometrial carcinoma. Knockdown and CRISPR/Cas9-mediated editing of reduced the cellular growth and colony-forming ability of K562 cells. CTCF knockdown also induced cell cycle arrest and a pro-survival response to apoptotic insult. However, in p53 shRNA-immortalised MEFs we observed the opposite: increased cellular proliferation, colony formation, cell cycle progression, and decreased survival after apoptotic insult compared to wild-type MEFs. CRISPR/Cas9-mediated targeting in MEFs revealed a predominance of in-frame microdeletions in in surviving clones, however protein expression could not be ablated. Examination of mutations in endometrial cancers showed locus-specific alterations in gene expression due to haploinsufficiency, in concert with downregulation of tumour suppressor genes and upregulation of estrogen-responsive genes. Depletion of CTCF expression imparts a dramatic negative effect on normal cell function. However, CTCF haploinsufficiency can have growth-promoting effects consistent with known cancer hallmarks in the presence of additional genetic hits. Our results confirm the absolute requirement for CTCF expression in somatic cells and provide definitive evidence of 's role as a haploinsufficient tumour suppressor gene. genetic alterations in endometrial cancer indicate that gene dysregulation is a likely consequence of loss, contributing to, but not solely driving cancer growth.