8 research outputs found
Aberrant Receptor Internalization and Enhanced FRS2-dependent Signaling Contribute to the Transforming Activity of the Fibroblast Growth Factor Receptor 2 IIIb C3 Isoform*
Alternative splice variants of fibroblast growth factor receptor 2 (FGFR2)
IIIb, designated C1, C2, and C3, possess progressive reduction in their
cytoplasmic carboxyl termini (822, 788, and 769 residues, respectively), with
preferential expression of the C2 and C3 isoforms in human cancers. We
determined that the progressive deletion of carboxyl-terminal sequences
correlated with increasing transforming potency. The highly transforming C3
variant lacks five tyrosine residues present in C1, and we determined that the
loss of Tyr-770 alone enhanced FGFR2 IIIb C1 transforming activity. Because
Tyr-770 may compose a putative YXXL sorting motif, we hypothesized
that loss of Tyr-770 in the 770YXXL motif may cause
disruption of FGFR2 IIIb C1 internalization and enhance transforming activity.
Surprisingly, we found that mutation of Leu-773 but not Tyr-770 impaired
receptor internalization and increased receptor stability and activation.
Interestingly, concurrent mutations of Tyr-770 and Leu-773 caused 2-fold
higher transforming activity than caused by the Y770F or L773A single
mutations, suggesting loss of Tyr and Leu residues of the
770YXXL773 motif enhances FGFR2 IIIb
transforming activity by distinct mechanisms. We also determined that loss of
Tyr-770 caused persistent activation of FRS2 by enhancing FRS2 binding to
FGFR2 IIIb. Furthermore, we found that FRS2 binding to FGFR2 IIIb is required
for increased FRS2 tyrosine phosphorylation and enhanced transforming activity
by Y770F mutation. Our data support a dual mechanism where deletion of the
770YXXL773 motif promotes FGFR2 IIIb C3
transforming activity by causing aberrant receptor recycling and stability and
persistent FRS2-dependent signaling
Genome-Scale Analysis Reveals Sst2 as the Principal Regulator of Mating Pheromone Signaling in the Yeast Saccharomyces cerevisiae
A common property of G protein-coupled receptors is that they become less responsive with prolonged stimulation. Regulators of G protein signaling (RGS proteins) are well known to accelerate G protein GTPase activity and do so by stabilizing the transition state conformation of the G protein α subunit. In the yeast Saccharomyces cerevisiae there are four RGS-homologous proteins (Sst2, Rgs2, Rax1, and Mdm1) and two Gα proteins (Gpa1 and Gpa2). We show that Sst2 is the only RGS protein that binds selectively to the transition state conformation of Gpa1. The other RGS proteins also bind Gpa1 and modulate pheromone signaling, but to a lesser extent and in a manner clearly distinct from Sst2. To identify other candidate pathway regulators, we compared pheromone responses in 4,349 gene deletion mutants representing nearly all nonessential genes in yeast. A number of mutants produced an increase (sst2, bar1, asc1, and ygl024w) or decrease (cla4) in pheromone sensitivity or resulted in pheromone-independent signaling (sst2, pbs2, gas1, and ygl024w). These findings suggest that Sst2 is the principal regulator of Gpa1-mediated signaling in vivo but that other proteins also contribute in distinct ways to pathway regulation
Synthesis and electrical properties of single crystalline CrSi2 nanowires
Free-standing CrSi2 nanowires are synthesized by a vapor transport based method for the first time. High-quality CrSi2 nanowires with a hexagonal cross section are produced by the reaction of a CrCl2 precursor and a Si substrate without using any metal catalyst. We have studied the crystal structure and electrical transport properties of CrSi2 nanowires. Transmission electron microscopy and X-ray diffraction studies confirm the single-crystalline nature of the CrSi2 nanowires of a C40 type structure. Four-probe devices were fabricated by the focused ion beam equipped with a nanomanipulator. Measured resistivity of the nanowire is 0.012 Omega center dot cm, which is close to that of bulk single-crystalline CrSi2close444