Functional roles of Grainyhead-like transcription factors in renal development and disease

Grainyhead-like 2 Deficiency and Kidney Cyst Growth in a Mouse Model

Key Points

Our study reveals segment-specific mechanisms in cystic kidney disease and suggests Grhl2 as a modifier of collecting duct–derived cyst progression. Our data demonstrate that genetic deletion of Grhl2 accelerates disease progression in a cystic mouse model.

Background

The transcription factor grainyhead-like 2 (GRHL2) plays a crucial role in maintaining the epithelial barrier properties of the kidney collecting duct and is important to osmoregulation. We noticed a reduction in GRHL2 expression in cysts derived from the collecting ducts in kidneys affected by autosomal dominant polycystic kidney disease (ADPKD). However, the specific role of GRHL2 in cystic kidney disease remains unknown.

Methods

The functional role of the transcription factor Grhl2 in the context of cystic kidney disease was examined through analysis of its expression pattern in patient samples with ADPKD and generating a transgenic cystic kidney disease (TCKD) mouse model by overexpressing the human proto-oncogene c-MYC in kidney collecting ducts. Next, TCKD mice bred with collecting duct–specific Grhl2 knockout mice (Grhl2KO). The resulting TCKD-Grhl2 KO mice and their littermates were examined by various types of histological and biochemical assays and gene profiling analysis through RNA sequencing.

Results

A comprehensive examination of kidney samples from patients with ADPKD revealed GRHL2 downregulation in collecting duct–derived cyst epithelia. Comparative analysis of TCKD and TCKD-Grhl2 KO mice exhibited that the collecting duct–specific deletion of Grhl2 resulted in markedly aggravated cyst growth, worsened kidney dysfunction, and shortened life span. Furthermore, transcriptomic analyses indicated sequential downregulation of kidney epithelial cyst development regulators (Frem2 , Muc1 , Cdkn2c , Pkd2 , and Tsc1 ) during cyst progression in kidneys of TCKD-Grhl2 KO mice, which included presumed direct Grhl2 target genes.

Conclusions

These results suggest Grhl2 as a potential progression modifier, especially for cysts originating from collecting ducts.

FOXA2 controls the anti-oxidant response in FH-deficient cells

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a cancer syndrome caused by inactivating germline mutations in fumarate hydratase (FH) and subsequent accumulation of fumarate. Fumarate accumulation leads to profound epigenetic changes and the activation of an anti-oxidant response via nuclear translocation of the transcription factor NRF2. The extent to which chromatin remodeling shapes this anti-oxidant response is currently unknown. Here, we explored the effects of FH loss on the chromatin landscape to identify transcription factor networks involved in the remodeled chromatin landscape of FH-deficient cells. We identify FOXA2 as a key transcription factor that regulates anti-oxidant response genes and subsequent metabolic rewiring cooperating without direct interaction with the anti-oxidant regulator NRF2. The identification of FOXA2 as an anti-oxidant regulator provides additional insights into the molecular mechanisms behind cell responses to fumarate accumulation and potentially provides further avenues for therapeutic intervention for HLRCC.

Grainyhead-like (Grhl) Target Genes in Development and Cancer

Grainyhead-like (GRHL) factors are essential, highly conserved transcription factors (TFs) that regulate processes common to both natural cellular behaviours during embryogenesis, and de-regulation of growth and survival pathways in cancer. Serving to drive the transcription, and therefore activation of multiple co-ordinating pathways, the three GRHL family members (GRHL1-3) are a critical conduit for modulating the molecular landscape that guides cellular decision-making processes during proliferation, epithelial-mesenchymal transition (EMT) and migration. Animal models and in vitro approaches harbouring GRHL loss or gain-of-function are key research tools to understanding gene function, which gives confidence that resultant phenotypes and cellular behaviours may be translatable to humans. Critically, identifying and characterising the target genes to which these factors bind is also essential, as they allow us to discover and understand novel genetic pathways that could ultimately be used as targets for disease diagnosis, drug discovery and therapeutic strategies. GRHL1-3 and their transcriptional targets have been shown to drive comparable cellular processes in Drosophila, C. elegans, zebrafish and mice, and have recently also been implicated in the aetiology and/or progression of a number of human congenital disorders and cancers of epithelial origin. In this review, we will summarise the state of knowledge pertaining to the role of the GRHL family target genes in both development and cancer, primarily through understanding the genetic pathways transcriptionally regulated by these factors across disparate disease contexts.