Sabino, J. C. | Search bioRxiv

bioRxiv2021

Epigenetic reprogramming by TET enzymes impacts co-transcriptional R-loops

DNA oxidation by ten-eleven translocation (TET) family enzymes is essential for epigenetic reprogramming. The conversion of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) initiates developmental and cell-type-specific transcriptional programs through mechanisms that include changes in the chromatin structure. Here, we show that the presence of 5hmC in the transcribed DNA promotes the annealing of the nascent RNA to its template DNA strand, leading to the formation of an R-loop. The genome-wide distribution of 5hmC and R-loops show a positive correlation in mouse and human embryonic stem cells and overlap in half of all active genes. Moreover, R-loop resolution leads to differential expression of a subset of genes that are involved in crucial events during stem cell proliferation. Altogether, our data reveal that epigenetic reprogramming via TET activity promotes co-transcriptional R-loop formation, and disclose novel links between R-loops and the regulation of gene expression programs in stem cells.

molecular biology↗

bioRxiv2020

Reduced nuclear lamin A/C enhances cancer cell squeezing through rigid barriers, does not facilitate endothelial crossing, and impairs experimental metastasis

The mechanisms by which the nuclear lamina of tumor cells controls their migration and survival are poorly understood. Lamin A and its variant lamin C are key nuclear lamina proteins that control nucleus stiffness and chromatin conformation. Downregulation of lamin A/C levels in two metastatic lines, B16F10 melanoma and E0771 breast carcinoma, facilitated cell squeezing through rigid pores, elevated nuclear deformability and reduced heterochromatin. Unexpectedly, the transendothelial migration of both cancer cells in vitro and in vivo, through lung capillaries, was not elevated by lamin A/C knockdown. Both cancer cells with lamin A/C knockdown grew normally in primary tumors and in vitro on rigid surfaces. Strikingly, however, both lamin A/C deficient melanoma and breast cancer cells grew poorly in 3D spheroids expanded in soft agar cultures. Experimental lung metastasis of both lamin A/C knockdown cells was also markedly reduced. Taken together, our results suggest that high content of lamin A/C in multiple cancer cells promotes cancer cell survival and ability to generate lung metastasis without compromising cancer cell emigration from lung vessels.

cancer biology↗