High impact information on CLA4

• Despite a cytokinesis defect, cla4 mutants are viable [1].
• In addition, Cla4 induces phosphorylation of Cdc24, leading to its dissociation from Bem1 at bud tips, thereby ending polarized bud growth in vivo [2].
• This defect is greatly exacerbated when combined with GTP binding-defective septins; conversely, the septin collar assembly defect of such mutants is suppressed efficiently by CLA4 overexpression [3].
• Although the precise mechanism of APC inhibition by Cla4t remains to be elucidated, our results suggest that Cla4 and Ste20 may regulate the first wave of cyclinB proteolysis mediated by Cdc20/APC, which has been shown to be crucial for activation of the mitotic exit network (MEN) [4].
• Cla4-green fluorescent protein localized to sites where the cortical actin cytoskeleton and cell surface growth are polarized, independently of an intact actin cytoskeleton [5].

Biological context of CLA4

• Thus, septin collar formation may correspond to septin filament assembly, and requires both GTP binding and Cla4-mediated phosphorylation of septins [3].
• The specific activity of Cla4p was cell cycle regulated, peaking near mitosis [6].
• In cultures started with unbudded cells, an inhibitor of Chs3p activity, nikkomycin Z, aggravated the abnormalities of cla4 and cdc11 mutants and gave rise to enlarged necks at the mother-bud junction, leading to cell death [7].
• Loss of Ste20 or Cla4 individually confers distinct phenotypes, implying that they regulate different processes [8].
• The results indicate that CLA4 is a single-copy gene located on the chromosome V of Y. lipolytica [9].

Anatomical context of CLA4

• A strain lacking a functional CLA4 gene exhibits an aberrant distribution of chitin in the cell wall, indicating a possible role for the Cla4 protein kinase in the maintenance of cell polarity in Y. lipolytica [9].
• Our results suggest that polarisome components and Cla4p are required for the initial assembly of the septin ring and that the actin cytoskeleton is involved in this process [10].
• This indicated that the plasma membrane pool of PI4P, but not phosphatidylinositol 4,5-bisphosphate or the Golgi pool of PI4P, is required for localization of Cla4 to sites of polarized growth [11].

Associations of CLA4 with chemical compounds

• Rather, we found that polarized growth induced by mutations in CDC12 and CLA4 or by expression of excess SWE1 was also sensitive to EDTA treatment and was restored by the addition of MnCl(2) but not by the addition of CaCl(2) [12].
• Remarkably, the substitution of a single amino acid, threonine 818, from Ste20 into an otherwise wild-type Cla4, Cla4D772T, conferred the ability to perform many Ste20-specific functions [13].
• Here we show that the p21-activated protein kinase-related kinase Cla4 of yeast integrates signaling by Cdc42 and phosphatidylinositol 4-phosphate (PI4P) [11].
• We found that the Cla4 pleckstrin homology (PH) domain binds in vitro to several phosphoinositide species [11].

Physical interactions of CLA4

• The identification of Pcl1-interacting proteins that genetically interact with Cla4 may indicate a link between G1 progression and mitotic exit [8].
• A combination of the Cdc42-binding and PH domains of Cla4 was necessary and sufficient for localization to sites of polarized growth [11].

Regulatory relationships of CLA4

• Cla4p kinase was activated in vivo by the GTP-bound form of Cdc42p [6].
• Specifically, Cdc42(D38E)p showed reduced interactions with the Cla4p p21-activated protein kinase and the Bem3p GTPase-activating protein and cdc42(D38E) was the only mutant allele able to complement the Deltacdc42 null mutant [14].
• Furthermore, when overexpressed, CLA4 induces Lte1 phosphorylation and localization to regions of polarized growth [15].
• Evidence is presented which suggests that the hyperphosphorylated form of Cla4 is responsible for relaying the signal to activate Gin4 [16].

Other interactions of CLA4

• Absence of a p21-activated protein kinase (Cla4) perturbs septin collar formation [3].
• Cla4p is homologous to mammalian p21-activated kinases (PAKs) (kinases activated by the rho-class GTPase Rac or Cdc42) [6].
• This effect was also seen when similarly truncated versions of Ste20p or Cla4p were overexpressed [17].
• Here, we identify a genetic interaction between PHO85, which encodes a cyclin-dependent kinase, and CLA4 [8].
• First, CLA4 and SIT4 were synthetically lethal [18].

Analytical, diagnostic and therapeutic context of CLA4

• PCR analysis with primers specific for serotype A or D alleles of the CNA1, CLA4, and GPA1 genes revealed that both alleles are often present in serotype AD strains [19].

References