The juxtamembrane region of the epidermal growth factor receptor is required for phosphorylation of Galpha(s).

We have previously demonstrated that Galpha(s) associates with the juxtamembrane region of the epidermal growth factor (EGF) receptor (EGFR) and that the EGFR can phosphorylate and activate this G protein (H. Poppleton et al., 1996, J. Biol. Chem. 271, 6947-6951; H. Sun et al., 1995, Proc. Natl. Acad. Sci. USA 92, 2229-2233). In this report, we have employed peptides EGFR-13 and EGFR-14 (corresponding to amino acids 645-657 and 679-692 in the EGFR, respectively) which disrupt the association of Galpha(s) with the EGFR to investigate whether or not this region of the EGFR is required for phosphorylation of the G protein. EGFR-13 increased the tyrosine phosphorylation of G(alpha)s by two-fold whereas EGFR-14 decreased the phosphorylation of the G protein. Phosphorylation of EGFR-13 on the threonine residue corresponding to Thr654 of the EGFR obliterated the ability of the peptide to increase Galpha(s) phosphorylation. EGFR-13 and EGFR-14, but not phospho-EGFR-13, competed for the association of the EGFR with Galpha(s). A peptide betaIII-2 corresponding to amino acids Arg259-Lys273 in the beta2-adrenergic receptor which competes for association of Galpha(s) with the EGFR and increases protein tyrosine kinase activity of the EGFR could mimic the effects of EGFR-13. Among the three peptides (EGFR-13, EGFR-14, and betaIII-2) that interfere with association of Galpha(s) to the EGFR, only EGFR-13 and betaIII-2 have been shown to activate the G protein. Polylysine which increases EGFR tyrosine kinase activity but does not interfere with association of Galpha(s) and EGFR also augmented phosphorylation of Galpha(s) by the EGFR. Phosphopeptide mapping demonstrated that EGFR-13 and polylysine increased phosphorylation of Galpha(s) by the EGFR on the same additional sites. Collectively, these data suggest that the interaction of Galpha(s) with residues 645-657 of the EGFR, or a peptide corresponding to this sequence alters the conformation of the G protein and/or the EGFR such that Galpha(s) is readily phosphorylated by the EGFR. The peptide EGFR-14, which does not activate Galpha(s), does not allow for the efficient phosphorylation of the G protein even though it does elevate the intrinsic tyrosine kinase activity of the EGFR. The hyperphosphorylation of Galpha(s) by EGFR is likely to require the contact of the G protein with EGFR-13 region (aa 645-657 in the EGFR) as well as augmentation of EGFR kinase activity.

Transmodulation of epidermal growth factor receptor function by cyclic AMP-dependent protein kinase.

Binding of epidermal growth factor (EGF) to its receptor (EGFR) augments the tyrosine kinase activity of the receptor and autophosphorylation. Exposure of some tissues and cells to EGF also stimulates adenylyl cyclase activity and results in an increase in cyclic AMP (cAMP) levels. Because cAMP activates the cAMP-dependent protein kinase A (PKA), we investigated the effect of PKA on the EGFR. The purified catalytic subunit of PKA (PKAc) stoichiometrically phosphorylated the purified full-length wild type (WT) and kinase negative (K721M) forms of the EGFR. PKAc phosphorylated both WT-EGFR as well as a mutant truncated form of EGFR (Delta1022-1186) exclusively on serine residues. Moreover, PKAc also phosphorylated the cytosolic domain of the EGFR (EGFRKD). Phosphorylation of the purified WT as well as EGFRDelta1022-1186 and EGFRKD was accompanied by decreased autophosphorylation and diminished tyrosine kinase activity. Pretreatment of REF-52 cells with the nonhydrolyzable cAMP analog, 8-(4-chlorophenylthio)-cAMP, decreased EGF-induced tyrosine phosphorylation of cellular proteins as well as activation of the WT-EGFR. Similar effects were also observed in B82L cells transfected to express the Delta1022-1186 form of EGFR. Furthermore, activation of PKAc in intact cells resulted in serine phosphorylation of the EGFR. The decreased phosphorylation of cellular proteins and diminished activation of the EGFR in cells treated with the cAMP analog was not the result of altered binding of EGF to its receptors or changes in receptor internalization. Therefore, we conclude that PKA phosphorylates the EGFR on Ser residues and decreases its tyrosine kinase activity and signal transduction both in vitro and in vivo.

Facilitation of signal onset and termination by adenylyl cyclase.

The alpha subunit (Gsalpha) of the stimulatory heterotrimeric guanosine triphosphate binding protein (G protein) Gs activates all isoforms of mammalian adenylyl cyclase. Adenylyl cyclase (Type V) and its subdomains, which interact with Gsalpha, promoted inactivation of the G protein by increasing its guanosine triphosphatase (GTPase) activity. Adenylyl cyclase and its subdomains also augmented the receptor-mediated activation of heterotrimeric Gs and thereby facilitated the rapid onset of signaling. These findings demonstrate that adenylyl cyclase functions as a GTPase activating protein (GAP) for the monomeric Gsalpha and enhances the GTP/GDP exchange factor (GEF) activity of receptors.

Identification of an intramolecular interaction between small regions in type V adenylyl cyclase that influences stimulation of enzyme activity by Gsalpha.

Using the full-length and two engineered soluble forms (C1-C2 and Cla-C2) of type V adenylyl cyclase (ACV), we have investigated the role of an intramolecular interaction in ACV that modulates the ability of the alpha subunit of the stimulatory GTP-binding protein of AC (Gsalpha) to stimulate enzyme activity. Concentration-response curves with Gsalpha suggested the presence of high and low affinity sites on ACV, which interact with the G protein. Activation of enzyme by Gsalpha interaction at these two sites was most apparent in the C1a-C2 form of ACV, which lacks the C1b region (K572-F683). Yeast two-hybrid data demonstrated that the C1b region interacted with the C2 region and its 64-aa subdomain, C2I. Using peptides corresponding to the C2I region of ACV, we investigated the role of the C1b/C2I interaction on Gsalpha-mediated stimulation of C1-C2 and full-length ACV. Our data demonstrate that a 10-aa peptide corresponding to L1042-T1051 alters the profile of the activation curves of full-length and C1-C2 forms of ACV by different Gsalpha concentrations to mimic the activation profile observed with C1a-C2 ACV. The various peptides used in our studies did not alter forskolin-mediated stimulation of full-length and C1-C2 forms of ACV. We conclude that the C1b region of ACV interacts with the 10-aa region (L1042-T1051) in the C2 domain of the enzyme to modulate Gsalpha-elicited stimulation of activity.

Characterization of soluble forms of nonchimeric type V adenylyl cyclases.

Type V adenylyl cyclase (ACV) belongs to the family of Ca2+-inhibited cyclases. We have generated two soluble forms of the enzyme containing the C1 or C1a region (which lacks the C-terminal 112 amino acids) linked to the C2 domain and compared their regulation with the full-length ACV. All three forms of ACV were stimulated by the alpha subunit of the stimulatory G protein Gs (G(s alpha)) and forskolin. However, the synergistic stimulation by both these activators was markedly enhanced in the soluble enzymes. Moreover, the alpha subunit of the inhibitory G protein Gi (G(i alpha)) inhibited all forms of the enzyme, indicating that the regions for G(s alpha) and G(i alpha) interaction are preserved in the soluble forms. Ca2+ inhibited forskolin-stimulated adenylyl cyclase (AC) activity of the full-length and C1-C2 forms of ACV but did not alter the activity of the C1a-C2 form. Maximal stimulation of AC activity by combination of G(s alpha) and forskolin obliterated the Ca2+-mediated inhibition of the full-length and C1-C2 forms of ACV. In 45Ca2+ overlay experiments, the C1-C2 but not the C1a-C2 soluble ACV bound Ca2+. Moreover, proteins corresponding to the C1a and C2 domains did not bind calcium. On the other hand, the proteins corresponding to C1 and its C-terminal 112 amino acids (C1b) bound 45Ca2+. To our knowledge, this is the first report of nonchimeric soluble forms of AC in which regulation by G(s alpha) and G(i alpha) is preserved. Moreover, we demonstrate that the 112 amino acid C1b region of ACV is responsible for the binding of Ca2+ and inhibition of enzyme activity.

Evaluation of the CDC gravid trap for the surveillance of St. Louis encephalitis vectors in Memphis, Tennessee.

Collections with CDC Gravid Mosquito Traps on 954 trap-nights from May through September 1983 are compared to 2,608 concurrent resting site collections made in the same area of Memphis, Tennessee. Gravid Traps yielded 88 times more Culex per collection and 96 times more Culex per man hour. The total Gravid Trap catch was 135,724 mosquitoes, 99% of which were either Culex pipiens or Cx. restuans, whereas these species comprised only 63% of the 6,613 mosquitoes collected from resting sites. Gravid Traps also collected significant numbers of Aedes aegypti and Ae. triseriatus. On most nights, more than 95% of mosquitoes in the Gravid Trap catch were gravid females. These results demonstrate that the trap is an effective and efficient device for collecting several important vector species. The preponderance of gravid mosquitoes should enhance the probability of encountering pathogens acquired by blood-feeding.