Entezari, A. A. | bioRxiv Science

bioRxiv2026

p38α MAPK integrates opposing oncogenic APC/β-catenin/TCF and GUCY2C tumor-suppressor axes in colorectal cancer

Introduction: Sporadic colorectal cancers (CRCs) form following initiating APC mutations, inducing constitutive {beta}-catenin/TCF signaling. Similarly, the guanylyl cyclase C (GUCY2C) tumor suppressor axis is universally silenced in CRC. While the GUCY2C receptor is retained, loss of its paracrine hormones guanylin (GUCA2A) and uroguanylin (GUCA2B) is among the earliest events in transformation. Mutant APC/{beta}-catenin/TCF signaling driving CRC transcriptionally silences GUCY2C hormone expression while suppressing that oncogenic pathway reconstitutes hormone production opposing tumorigenesis. p38 opposes tumor initiation, and its loss promotes transformation in chemical and genetic mouse models of CRC. In healthy intestine, p38 supports a gradient of epithelial differentiation along the crypt-surface axis. Here, we reveal that p38 links regulation of oncogenic APC/{beta}-catenin/TCF signaling and GUCY2C hormone expression. Methods: Regulation of p38 by APC/{beta}-catenin/TCF signaling was defined in four genetically engineered human CRC cell lines with conditional oncogenic APC/{beta}-catenin/TCF signaling and healthy human colon organoids. Expression of p38 was eliminated from conditional human CRC cell lines by pharmacological inhibition, RNA knockdown, and CRISPR/Cas9 gene editing. Transcriptomic analysis of these cells by RNA sequencing defined the set of genes regulated by APC/{beta}-catenin/TCF signaling controlled through p38. Results: In CRC cell lines, APC/{beta}-catenin/TCF signaling suppressed p38 phosphorylation and activity, whereas inhibition of APC/{beta}-catenin/TCF restored p38 signaling. In the absence of APC/{beta}-catenin/TCF signaling, inhibiting p38 repressed GUCY2C hormone expression. Inhibiting APC/{beta}-catenin/TCF signaling enriched phosphorylated p38 at the GUCA2A promoter. In that context, analysis of the CPTAC proteomic database revealed that phosphorylation of p38 and its upstream kinases MKK3 and MKK4 was reduced in human CRC. Finally, transcriptomic analysis revealed that p38 is a critical signaling node controlling the expression of a substantial subset of APC/{beta}-catenin/TCF-regulated genes in human CRC cells and patient tumors. Conclusions: APC/{beta}-catenin/TCF signaling inhibits p38 phosphorylation and transcriptional activity, suppressing GUCA2A and GUCA2B expression and functionally silencing the retained GUCY2C receptor. These findings identify p38 as a signaling intermediary integrating oncogenic APC/{beta}-catenin/TCF activity to extinction of the GUCY2C tumor-suppressor axis and reveal a broader p38-dependent component of the APC/{beta}-catenin/TCF-regulated transcriptome.

cancer biology↗

bioRxiv2019

Natural variants in C. elegans atg-5 3’UTR uncover divergent effects of autophagy on polyglutamine aggregation in different tissues

Diseases caused by protein misfolding and aggregation, in addition to cell selectivity, often exhibit variation among individuals in the age of onset, progression, and severity of disease. Genetic variation has been shown to contribute to such clinical variation. We have previously found that protein aggregation-related phenotypes in a model organism, C. elegans, can be modified by destabilizing polymorphisms in the genetic background and by natural genetic variation. Here, we identified a large modifier locus in a Californian wild strain of C. elegans, DR1350, that alters the susceptibility of the head muscle cells to polyglutamine (polyQ) aggregation, and causes an increase in overall aggregation, without changing the basal activity of the muscle proteostasis pathways known to affect polyQ aggregation. We found that the two phenotypes were genetically separable, and identified regulatory variants in a gene encoding a conserved autophagy protein ATG-5 (ATG5 in humans) as being responsible for the overall increase in aggregation. The atg-5 gene conferred a dosage-dependent enhancement of polyQ aggregation, with DR1350-derived atg-5 allele behaving as a hypermorph. Examination of autophagy in animals bearing the modifier locus indicated enhanced response to an autophagy-activating treatment. Because autophagy is known to be required for the clearance of polyQ aggregates, this result was surprising. Thus, we tested whether directly activating autophagy, either pharmacologically or genetically, affected the polyQ aggregation in our model. Strikingly, we found that the effect of autophagy on polyQ aggregation was tissue-dependent, such that activation of autophagy decreased polyQ aggregation in the intestine, but increased it in the muscle cells. Our data show that cryptic genetic variants in genes encoding proteostasis components, although not causing visible phenotypes under normal conditions, can have profound effects on the behavior of aggregation-prone proteins, and suggest that activation of autophagy may have divergent effects on the clearance of such proteins in different cell types.

genetics↗