Functional Characterization of the MKC1 Gene of Candida albicans, Which Encodes a Mitogen-Activated Protein Kinase Homolog Related to Cell Integrity

Abstract

Mitogen-activated protein (MAP) kinases represent a group of serine/threonine protein kinases playing a central role in signal transduction processes in eukaryotic cells. Using a strategy based on the complementation of the thermosensitive autolytic phenotype of slt2 null mutants, we have isolated a Candida albicans homolog of Saccharomyces cerevisiae MAP kinase gene SLT2 (MPK1), which is involved in the recently outlined PKC1-controlled signalling pathway. The isolated gene, named MKC1 (MAP kinase from C. albicans), coded for a putative protein, Mkc1p, of 58,320 Da that displayed all the characteristic domains of MAP kinases and was 55% identical to S. cerevisiae Slt2p (Mpk1p). The MKC1 gene was deleted in a diploid Candida strain, and heterozygous and homozygous strains, in both Ura ؉ and Ura ؊ backgrounds, were obtained to facilitate the analysis of the function of the gene. Deletion of the two alleles of the MKC1 gene gave rise to viable cells that grew at 28 and 37؇C but, nevertheless, displayed a variety of phenotypic traits under more stringent conditions. These included a low growth yield and a loss of viability in cultures grown at 42؇C, a high sensitivity to thermal shocks at 55؇C, an enhanced susceptibility to caffeine that was osmotically remediable, and the formation of a weak cell wall with a very low resistance to complex lytic enzyme preparations. The analysis of the functions downstream of the MKC1 gene should contribute to understanding of the connection of growth and morphogenesis in pathogenic fungi.

Candida albicans strains heterozygous and homozygous for mutations in mitogen-activated protein kinase signaling components have defects in hyphal development

“…The lack of dominance of the wild-type allele to the null allele has also been reported for the Candida drug transporter CaMDR and the Candida MKC1 gene, a homolog of the Saccharomyces MAPK SLT2͞MPK1. The heterozygotes of null mutations of these genes are more sensitive to inhibitors than the wild type (23,24).…”

A role for the MAP kinase gene MKC1 in cell wall construction and morphological transitions in Candida albicans

“…cerevisiae. These genes, CST20 (STE20 homologue) (Kohler & Fink, 1996;Leberer et al, 1996), HST7 (STE7 homologue) (Kohler & Fink, 1996;Clark et al, 1995), CEKl (KSSl homologue) (Whiteway et al, 1992) and CPHl (STEl2 homologue) (Liu et al, 1994;Malathi et al, 1994) (Navarro-Garcia et al, 1995) and shown it to be essential for cell growth at high temperatures and thermal shock survival. In this work, we describe how deletion of M K C l results in cell wall defects in C. albicans, a result with potential applications in the search for new antifungal therapies and, in addition, we present evidence for a role for this transduction cascade in some cellular morphogenetic responses.…”

A MAP Kinase Pathway Is Implicated in the Pseudohyphal Induction by Hydrogen Peroxide in Candica albicans

“…Null mutants for any of these genes are defective in hyphal development on solid medium in response to inducers such as synthetic low ammonium; however, hyphae develop normally in response to serum (Csank et al, 1998;Leberer et al, 1996;Liu et al, 1994). Mkc1, the homologue of the S. cerevisiae Mpk1 MAPK, plays a role in maintaining cellular integrity and cell wall formation as deduced from the osmotically-remediable sensitivity of mutant cells to certain cell-wallinterfering compounds (Navarro-Garcia et al, 1995). We previously demonstrated that exogenous H 2 O 2 induces filamentous growth in C. albicans (Nasution et al, 2008).…”