Carbon catabolite repression (CCR) of several Bacillus subtilis catabolic genes is mediated by ATPdependent phosphorylation of histidine-containing protein (HPr), a phosphocarrier protein of the phosphoenolpyruvate (PEP): sugar phosphotransferase system. In this study, we report the discovery of a new B. subtilis gene encoding a HPr-like protein, Crh (for catabolite repression HPr), composed of 85 amino acids. Crh exhibits 45% sequence identity with HPr, but the active site His-15 of HPr is replaced with a glutamine in Crh. Crh is therefore not phosphorylated by PEP and enzyme I, but is phosphorylated by ATP and the HPr kinase in the presence of fructose-1,6-bisphosphate. We determined Ser-46 as the site of phosphorylation in Crh by carrying out mass spectrometry with peptides obtained by tryptic digestion or CNBr cleavage. In a B. subtilis ptsH1 mutant strain, synthesis of ␤-xylosidase, inositol dehydrogenase, and levanase was only partially relieved from CCR. Additional disruption of the crh gene caused almost complete relief from CCR. In a ptsH1 crh1 mutant, producing HPr and Crh in which Ser-46 is replaced with a nonphosphorylatable alanyl residue, expression of ␤-xylosidase was also completely relieved from glucose repression. These results suggest that CCR of certain catabolic operons requires, in addition to CcpA, ATP-dependent phosphorylation of Crh, and HPr at Ser-46.The bacterial phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS) catalyzes the transport and concomitant phosphorylation of carbohydrates via a protein phosphorylation chain including PEP-dependent phosphorylation of His-15 in histidine-containing protein (HPr) by enzyme I (EI). P-His-HPr phosphorylates the sugar-specific EIIAs. In Gram-positive bacteria, the PTS regulates also induction and carbon catabolite repression (CCR) of numerous catabolic genes (1). The central regulatory protein involved in these various functions is HPr. In Gram-positive bacteria, this small phosphoryl transfer protein can be phosphorylated at a regulatory serine (Ser-46) by ATP and the HPr kinase (2, 3), in addition to phosphorylation at the catalytic His-15 by PEP and EI (4, 5). PEP-dependent and ATP-dependent phosphorylation of HPr interfere with each other-i.e., P-His-HPr is a poor substrate for the HPr kinase and P-Ser-HPr is a poor substrate for EI (6, 7). ATP-dependent phosphorylation of HPr is stimulated by glycolytic intermediates such as fructose-1,6-bisphosphate (FBP) in Enterococcus faecalis (6) and in Streptococcus pyogenes (7). It has been reported that FBP is also implicated in CCR of the Bacillus subtilis gnt and iol operons (8, 9), and a potential role of phosphorylation of HPr at Ser-46 in CCR has therefore been investigated (10). The gnt operon contains the genes gntRKPZ encoding the repressor GntR, gluconate kinase, gluconate permease, and a gluconate-6-Pdehydrogenase (11), whereas the iol operon is composed of 10 genes encoding enzymes presumably implicated in inositol metabolism, including iolG encoding inositol dehydro...

Cells with stem-like properties, tumorigenic potential, and treatment-resistant phenotypes have been identified in many human malignancies. Based on the properties they share with nonneoplastic stem cells or their ability to initiate and propagate tumors in vivo, such cells were designated as cancer stem (stem-like) or tumor initiating/propagating cells. Owing to their implication in treatment resistance, cancer stem cells (CSCs) have been the subject of intense investigation in past years. Comprehension of CSCs' intrinsic properties and mechanisms they develop to survive and even enhance their aggressive phenotype within the hostile conditions of the tumor microenvironment has reoriented therapeutic strategies to fight cancer. This report provides selected examples of malignancies in which the presence of CSCs has been evidenced and briefly discusses methods to identify, isolate, and functionally characterize the CSC subpopulation of cancer cells. Relevant biological targets in CSCs, their link to treatment resistance, proposed targeting strategies, and limitations of these approaches are presented. Two major aspects of CSC physiopathology, namely, relative in vivo quiescence and plasticity in response to microenvironmental cues or treatment, are highlighted. Implications of these findings in the context of the development of new therapies are discussed.