Potential use of potassium efflux-deficient yeast for studying trafficking signals and potassium channel functions.

The activity of potassium (K(+)) channels critically depends on their density on the cell surface membrane, which is regulated by dynamic protein-protein interactions that often involve distinct trafficking signals on the cargo proteins. In this paper we explored the possibility of utilizing the Saccharomyces cerevisiae strain B31 for identification of the signal motifs that regulate surface expression of membrane proteins and for studying structure-function relationships of K(+) channels. B31 cells lack the K(+) efflux system and were reported to show overloaded K(+)-mediated growth inhibition in high K(+) media upon heterologous expression of a mammalian inwardly rectifying K(+) channel (Kir2.1). We show that while the expression of wild-type Kir2.1 channel inhibits the growth of B31 cells in high K(+) media, the human disease-causing mutations of Kir2.1 that abolish K(+) conduction (V302M) or surface trafficking (Δ314/315) fully restores the growth. The expression of two-pore-domain K(+) channel KCNK3 or KCNK9 also inhibited the growth of B31 in high K(+) media while C-terminal mutations that reduce their 14-3-3 protein-dependent cell surface trafficking restored the growth of B31. Finally, the expression of Kir2.1 channels that were C-terminally fused with known sequence motifs including ER retention/retrieval signals and an endocytosis signal allowed the growth of B31 in high K(+) media. These results demonstrate the potential of B31 yeast strain as a unique biological tool to screen the random peptide libraries for novel sequence signals that down-regulate surface expression of membrane proteins, as well as to systematically identify the structural determinants for cell surface trafficking and/or ion conductance of K(+) channels.

An independent confirmatory factor analysis of the Wechsler Intelligence Scale for Children-fourth Edition (WISC-IV) integrated: what do the process approach subtests measure?

The Wechsler intelligence scale for children--fourth edition (WISC-IV) Integrated contains the WISC-IV core and supplemental subtests along with process approach subtests designed to facilitate a process-oriented approach to score interpretation. The purpose of this study was to examine the extent to which WISC-IV Integrated subtests measure the constructs they are purported to measure. In addition to examining the measurement and scoring model provided in the manual, this study also tested hypotheses regarding Cattell-Horn-Carroll abilities that might be measured along with other substantive questions regarding the factor structure of the WISC-IV Integrated and the nature of abilities measured by process approach subtests. Results provide insight regarding the constructs measured by these subtests. Many subtests appear to be good to excellent measures of psychometric g (i.e., the general factor presumed to cause the positive correlation of mental tasks). Other abilities measured by subtests are described. For some subtests, the majority of variance is not accounted for by theoretical constructs included in the scoring model. Modifications made to remove demands such as memory recall and verbal expression were found to reduce construct-irrelevant variance. The WISC-IV Integrated subtests appear to measure similar constructs across ages 6-16, although strict factorial invariance was not supported.

The bisecting GlcNAc on N-glycans inhibits growth factor signaling and retards mammary tumor progression.

The branching of complex N-glycans attached to growth factor receptors promotes tumor progression by prolonging growth factor signaling. The addition of the bisecting GlcNAc to complex N-glycans by Mgat3 has varying effects on cell adhesion, cell migration, and hepatoma formation. Here, we show that Chinese hamster ovary cells expressing Mgat3 and the polyoma middle T (PyMT) antigen have reduced cell proliferation and growth factor signaling dependent on a galectin lattice. The Mgat3 gene is not expressed in virgin mammary gland but is upregulated during lactation and is expressed in mouse mammary tumor virus (MMTV)/PyMT tumors. Mice lacking Mgat3 that cannot transfer the bisecting GlcNAc to N-glycans acquire PyMT-induced mammary tumors more rapidly and have an increased tumor burden, increased migration of tumor cells, and increased early metastasis to lung. Tumors and tumor-derived cells lacking Mgat3 exhibit enhanced signaling through the Ras pathway and reduced amounts of functionally glycosylated alpha-dystroglycan. Constitutive overexpression of an MMTV/Mgat3 transgene inhibits early mammary tumor development and tumor cell migration. Thus, the addition of the bisecting GlcNAc to complex N-glycans of mammary tumor cell glycoprotein receptors is a cell autonomous mechanism serving to retard tumor progression by reducing growth factor signaling.