Gene links breast cancer to stress, circadian disruption

Two researchers from the Philippines have discovered a gene the connects breast cancer development to stress and body clock disruption. In a recent study, they have shown the mechanism behind hormone and circadian regulation of the tumour-suppressor gene, Krüppel-like factor 9 (KLF9), and its effect on breast cancer progression.

“To our knowledge, this study is the first to provide evidence for KLF9 in the consequential link between the hormone and circadian signaling networks towards breast cancer pathogenesis,” said molecular biologist Dr Pia Bagamasbad and her student Weand Ybañez, both from the University of the Philippines.

“Aberrant KLF9 expression and oscillation in breast cancer may disrupt the normal cycling dynamics of the entire circadian network as KLF9 can influence the hormone response of core cellular clock and clock output genes, ultimately resulting in tumorigenesis,” they added.

Bagamasbad and Ybañez performed a meta-analysis of publicly available RNA- and ChIP-sequencing datasets from breast cancer tumour samples and cell lines, as well as gene expression analysis by RT-qPCR and enhancer-reporter assays, to explore the molecular mechanism behind the clock and hormone regulation of KLF9.

They then generated lentiviral knockdown and overexpression of KLF9 in three distinct breast epithelial cell lines (MCF10A, MCF7 and MDA-MB-231) to explain the role of KLF9 in orthogonal assays on breast epithelial survival, proliferation, apoptosis, and migration.

According to Bagamasbad and Ybañez, KLF9 “suppresses the growth and spread of breast cancer cells,” but this gene has a cyclical pattern that is part of a healthy body clock. Thus, disruption of this body clock tends to reduce the gene’s capacity to prevent breast cancer progression. [https://bit.ly/3JklWD4]

KLF9 was found to be a direct glucocorticoid (GC) receptor target in mammary epithelial cells. Its induction was potentially mediated through coordinate transcriptional activation from several GC-responsive enhancers in the KLF9 locus. [Cancer Cell Int 2023;23:33]

Notably, the researchers observed the elimination of rhythmic expression of KLF9 in MCF10A cells in the highly aggressive MDA-MB-231 line. The forced expression of KLF9 then modified the baseline and GC/E2-responsive expression of several clock genes, suggesting the role of this gene as a regulator of the core clock machinery.

Using complementary cancer hallmark assays in the context of the hormone-circadian axis, Bagamasbad and Ybañez revealed the tumour-suppressive role of KLF9 in breast cancer regardless of molecular subtype. This gene explained the antitumour effects of GC in E2 receptor + luminal MCF7 cells, while preventing GC-enhanced oncogenicity in triple-negative MCF10A and MDA-MB-231 cells.

“Maladaptive alterations to hormone signaling that is prevalent in breast cancer result in dysregulated expression of hormone-regulated clock genes, cascading onto the entire circadian molecular network owing to its interdependent nature,” the researchers said. [Oncogene 2007;26:7916-7920; PLoS ONE 2014;9:e95878; Proc Natl Acad Sci USA 2009;106:17582-17587; J Biol Chem 2005;280:42036-42043]

“Disruption of the local mammary clock ultimately results in the aberrant circadian control of proliferation, metabolism, and invasive capacity, further exacerbating breast cancer progression,” they added. [Breast Cancer Res 2016;18:89; Front Endocrinol 2018;9:219]

“Our study marks a necessary first step in filling the crucial gap in knowledge of the key players in hormone-associated circadian disruption and breast cancer aetiology,” Bagamasbad and Ybañez said.