The seven-spanning calcium-sensing receptor (CaSR) activates multiple G proteins including Gq and Gi, and thereby activates a variety of second messengers and inhibits parathyroid hormone (PTH) secretion. However, the exact signaling mechanisms underlying the functional activity of CaSR are not yet fully understood. The heterozygous inactivation of CaSR or its inhibition by antibody blocking results in either familial hypocalciuric hypercalcemia or acquired hypocalciuric hypercalcemia (AHH), respectively. Here, we report the identification of a unique CaSR autoantibody in an AHH patient. Paradoxically, we find that this autoantibody potentiates the Ca 2؉ /Gq-dependent accumulation of inositol phosphates by slightly shifting the dose dependence curve of the Ca 2؉ mediated activation of phosphatidylinositol turnover to the left, whereas it inhibits the Ca 2؉ /Gi-dependent phosphorylation of ERK1/2 in HEK293 cells stably expressing human CaSR. Treatment of these same cells with a calcimimetic, NPS-R-568, augments the CaSR response to Ca 2؉ , increasing phosphatidylinositol turnover and ERK1/2 phosphorylation, and overcoming the autoantibody effects. Our observations thus indicate that a calcium-stimulated CaSR primed by a specific autoantibody adopts a unique conformation that activates Gq but not Gi. Our findings also suggest that CaSR signaling may act via both Gq and Gi to inhibit PTH secretion. This is the first report of a disease-related autoantibody that functions as an allosteric modulator and maintains G proteincoupled receptors (GPCRs) in a unique active conformation with its agonist. We thus speculate that physiological modulators may exist that enable an agonist to specifically activate only one signaling pathway via a GPCR that activates multiple signaling pathways.allosteric modulation ͉ disease ͉ functional selectivity ͉ G protein-coupled receptors ͉ multiple active conformations

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Background: cAMP-induced phosphorylation of RhoA has been considered to inhibit RhoA signaling, causing cell rounding. Results: Knockdown of RhoGDI␣ blocks cAMP-induced cell rounding, and RhoGDI␣-WT expression but not RhoGDI␣-S174A expression recovers. Conclusion: Phosphorylation of RhoGDI␣ likely inhibits RhoA by stabilizing a active RhoA-RhoGDI␣ complex. Significance: This may underlie G s /cAMP-induced cross-talk with G q /G 13 /RhoA signaling.

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The incidence of thyroid carcinoma has been increasing worldwide. This is interpreted as an increase in the incidental detection of papillary thyroid microcarcinomas (PTMCs). However, mortality has not changed, suggesting overdiagnosis and overtreatment. Prospective clinical trials of active surveillance for low-risk PTMC (T1aN0M0) have been conducted in two Japanese institutions since the 1990s. Based on the favorable outcomes of these trials, active surveillance has been gradually adopted worldwide. A task force on the management of PTMC in adults organized by the Japan Thyroid Association therefore conducted a systematic review and has produced the present position paper based on the scientific evidence concerning active surveillance. This paper indicates evidence for the increased incidence of PTMC, favorable surgical outcomes for low-risk PTMC, recommended criteria for diagnosis using fine needle aspiration cytology, and evaluation of lymph node metastasis (LNM), extrathyroidal extension (ETE) and distant metastasis. Active surveillance has also been reported with a low incidence of disease progression and no subsequent recurrence or adverse events on survival if conversion surgery was performed at a slightly advanced stage. Active surveillance is a safe and valid strategy for PTMC, because it might preserve physical quality of life and reduce 10-year medical costs. However, some points should be noted when performing active surveillance. Immediate surgery is needed for PTMC showing high-risk features, such as clinical LNM, ETE or distant metastasis. Active surveillance should be performed under an appropriate medical team and should be continued for life.

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Pseudohypoparathyroidism type Ia (PHP-Ia) results from the loss of one allele of G s␣, causing resistance to parathyroid hormone and other hormones that transduce signals via G s. Most Gs␣mutations cause the complete loss of protein expression, but some cause loss of function only, and these have provided valuable insights into the normal function of G proteins. Here we have analyzed a mutant G s␣ (␣s-AVDT) harboring AVDT amino acid repeats within its GDP/GTP binding site, which was identified in unique patients with PHP-Ia accompanied by neonatal diarrhea. Biochemical and intact cell analyses showed that ␣s-AVDT is unstable but constitutively active as a result of rapid GDP release and reduced GTP hydrolysis. This instability underlies the PHP-Ia phenotype. ␣s-AVDT is predominantly localized in the cytosol, but in rat and mouse small intestine epithelial cells (IEC-6 and DIF-12 cells) ␣s-AVDT was found to be localized predominantly in the membrane where adenylyl cyclase is present and constitutive increases in cAMP accumulation occur in parallel. The likely cause of this membrane localization is the inhibition of an activation-dependent decrease in ␣s palmitoylation. Upon the overexpression of acyl-protein thioesterase 1, however, ␣s-AVDT translocates from the membrane to the cytosol, and the constitutive accumulation of cAMP becomes attenuated. These results suggest that PHP-Ia results from the instability of ␣s-AVDT and that the accompanying neonatal diarrhea may result from its enhanced constitutive activity in the intestine. Hence, palmitoylation may control the activity and localization of G s␣ in a cell-specific manner.disease ͉ G protein ͉ lipid modification ͉ localization ͉ activity G protein diseases have revealed key pathways underlying physiologic regulation and the molecular mechanisms involved. Pseudohypoparathyroidism type Ia (PHP-Ia) is a classic example of such a disease and results from the heterozygous loss of function of G s␣ (1-4). In most cases, the loss of G s␣ function results from a loss of protein expression due to insertions, deletions, frameshift deletions, nonsense mutations, and splice junction mutations. In some cases, however, PHP-Ia occurs in the presence of G s␣ protein expression, and analyses of the corresponding mutations have greatly furthered our understanding of how G proteins function normally (5).The activity of G s␣ is cyclically regulated via two unidirectional steps, a GDP/GTP exchange and the hydrolysis of GTP (5-8). The agonist-occupied receptor accelerates GDP release from the ␣␤␥ trimer, which allows GTP to bind to the empty guanine nucleotide pocket of G ␣ and thus induce a conformational change that enables its dissociation from the receptor and ␤␥ subunit. The GTP-bound G ␣ and ␤␥ dimer transmit a signal until GTP is hydrolyzed, which then allows the GDP-bound G ␣ to bind and inactivate G ␤␥ .The defects resulting from G s␣ mutations that do not prevent protein expression but nevertheless result in the onset of PHP-Ia have now been elucidated at the molecular l...