Biology subjects

Floor, M.

Publications and source records attributed to Floor, M..

3 recordsLinked to original sources

bioRxiv2023

Separation-of-function mutants reveal the NF-κB-independent involvement of IκBα in the regulation of stem cell and oncogenic programs

We previously demonstrated that the NF-{kappa}B inhibitor I{kappa}B binds the chromatin together with PRC2 to regulate a subset of developmental- and stem cell-related genes. This alternative function has been elusive in both physiological and disease conditions because of the predominant role of I{kappa}B as a negative regulator of NF-{kappa}B. We here uniquely characterize specific residues of I{kappa}B that allow the generation of separation-of-function (SOF) mutants that are defective for either NF-{kappa}B-related (SOF{Delta}NF-{kappa}B) or chromatin-related (SOF{Delta}H2A,H4) activities. Expression of I{kappa}B SOF{Delta}NF-{kappa}B, but not SOF{Delta}H2A/H4, is sufficient to negatively regulate a specific stemness program in intestinal cells, thus rescuing the differentiation blockage imposed by I{kappa}B deficiency. In contrast, full I{kappa}B activity is required for regulating clonogenic/tumor-initiating activity of colorectal cancer cells. Our data indicate that SOF mutants represent an exclusive tool for studying I{kappa}B functions in physiology and disease, and identified I{kappa}B as a robust prognosis biomarker for human cancer.

cell biology↗

bioRxiv2023

Ancient loss of catalytic selenocysteine spurred convergent adaptation in a mammalian oxidoreductase

Selenocysteine (Sec), the 21st amino acid specified by the genetic code, is a rare selenium-containing residue found in the catalytic site of selenoprotein oxidoreductases. Sec is analogous to the common cysteine (Cys) amino acid but its selenium atom offers physicalchemical properties not provided by the corresponding sulfur atom in Cys. Catalytic sites with Sec in selenoproteins of vertebrates are under strong purifying selection but one enzyme, Glutathione Peroxidase 6 (GPX6), independently exchanged Sec for Cys less than one hundred million years ago in several mammalian lineages. We reconstructed and assayed these ancient enzymes before and after Sec was lost and up to today, and found them to have lost their classic ability to reduce hydroperoxides using glutathione (GSH). This loss of function, however, was accompanied by bursts of amino acid changes in the catalytic domain, with protein sites concertedly changing under positive selection across distant lineages abandoning Sec in GPX6. This demonstrates that when sulfur in Cys impairs catalysis a narrow evolutionary path is followed, with epistasis and pleiotropy leading to convergent evolution and triggering enzymatic properties likely beyond those in classic GPXs. These findings are an unusual example of adaptive convergence towards unexplored oxidoreductase functions during mammalian evolution.

molecular biology↗

bioRxiv2021

Dynamic association of IκBα to chromatin is regulated by acetylation and cleavage of histone H4

I{kappa}Bs exert a principal function as cytoplasmic inhibitors of the NF-kB transcription factors. Additional functions for I{kappa}B homologues have been described including association to chromatin and transcriptional regulatioin. Phosphorylated and SUMOylated I{kappa}B (pS-I{kappa}B) binds histones H2A and H4 in the stem and progenitor compartment of skin and intestine, but the mechanisms controlling its recruitment to chromatin are largely unstudied. We here show that serine 32-36 phosphorylation of I{kappa}B favors its binding with nucleosomes and demonstrated that p-I{kappa}B association to H4 is favored by acetylation at specific H4 lysine residues. N-terminal tail of H4 is lost during intestinal cell differentiation by proteolytic cleavage at residues 17-19 imposed ny trypsin or chymotrypsin, which interferes p-I{kappa}B binding. Paradoxically, inhibition of trypsin and chymotrypsin activity in HT29 cells increased p-I{kappa}B chromatin binding and impaired goblet cell differentiation, comparable to I{kappa}B deletion. Together our results indicate that dynamic binding of I{kappa}B to chromatin is a requirement for intestinal cell differentiation and provide a molecular base for the restricted nuclear distribution of p-I{kappa}B at specific stem cell compartments.

molecular biology↗