Bacterial pathogens have evolved a wide range of strategies to colonize and invade human organs, despite the presence of multiple host defense mechanisms. In this review, we will describe how pathogenic bacteria can adhere and multiply at the surface of host cells, how some bacteria can enter and proliferate inside these cells, and finally how pathogens may cross epithelial or endothelial host barriers and get access to internal tissues, leading to severe diseases in humans.

Human Endogenous Retroviruses are expected to be the remnants of ancestral infections of primates by active retroviruses that have thereafter been transmitted in a Mendelian fashion. Here, we derived in silico the sequence of the putative ancestral “progenitor” element of one of the most recently amplified family—the HERV-K family—and constructed it. This element, Phoenix, produces viral particles that disclose all of the structural and functional properties of a bona-fide retrovirus, can infect mammalian, including human, cells, and integrate with the exact signature of the presently found endogenous HERV-K progeny. We also show that this element amplifies via an extracellular pathway involving reinfection, at variance with the non-LTR-retrotransposons (LINEs, SINEs) or LTR-retrotransposons, thus recapitulating ex vivo the molecular events responsible for its dissemination in the host genomes. We also show that in vitro recombinations among present-day human HERV-K (also known as ERVK) loci can similarly generate functional HERV-K elements, indicating that human cells still have the potential to produce infectious retroviruses.

Significance: Small ubiquitin-related modifier (SUMO) is a posttranslational modification essential for many functions in eukaryotic cells. A better understanding of the role of this ubiquitin-like modification, identification of proteins modified by SUMO, and knowledge of the exact sites of SUMO conjugation are critical but remain experimentally challenging. We have developed an innovative proteomic strategy allowing proteome-wide identification of SUMOylation sites and quantification of cell SUMOylation changes in response to diverse stimuli. Identification of yet unknown SUMO targets and characterization of SUMOylome alterations in response to environmental stresses, drugs, toxins, or bacterial and viral infections will help decipher previously unidentified roles of SUMOylation in cell physiology and disease.