Myosin vc interacts with Rab32 and Rab38 proteins and works in the biogenesis and secretion of melanosomes.

Class V myosins are actin-based motors with conserved functions in vesicle and organelle trafficking. Herein we report the discovery of a function for Myosin Vc in melanosome biogenesis as an effector of melanosome-associated Rab GTPases. We isolated Myosin Vc in a yeast two-hybrid screening for proteins that interact with Rab38, a Rab protein involved in the biogenesis of melanosomes and other lysosome-related organelles. Rab38 and its close homolog Rab32 bind to Myosin Vc but not to Myosin Va or Myosin Vb. Binding depends on residues in the switch II region of Rab32 and Rab38 and regions of the Myosin Vc coiled-coil tail domain. Myosin Vc also interacts with Rab7a and Rab8a but not with Rab11, Rab17, and Rab27. Although Myosin Vc is not particularly abundant on pigmented melanosomes, its knockdown in MNT-1 melanocytes caused defects in the trafficking of integral membrane proteins to melanosomes with substantially increased surface expression of Tyrp1, nearly complete loss of Tyrp2, and significant Vamp7 mislocalization. Knockdown of Myosin Vc in MNT-1 cells more than doubled the abundance of pigmented melanosomes but did not change the number of unpigmented melanosomes. Together the data demonstrate a novel role for Myosin Vc in melanosome biogenesis and secretion.

Farmers' production constraints, preferred varietal traits and perceptions on sorghum grain mold in Senegal.

Improving sorghum adoption rates by developing adapted varieties that meet end-user preferences is a major challenge in West Africa. In this study, a participatory rural appraisal was undertaken to identify the main sorghum production constraints, farmers' preferred variety traits and their perceptions on sorghum grain mold. The study was conducted in four representative rural communities located in the main sorghum producing area of Senegal. A total of 260 farmers were interviewed and data were collected through focus group discussions and individual questionnaires. Our results indicated that Striga, insects, poor soil fertility and drought are the major sorghum producing constraints in Senegal. Grain mold was identified as the second most important sorghum disease after the damping-off. Discoloration on grain surface was the most important criteria farmers used to recognize the disease. The most important sorghum traits farmers desired in improved varieties are medium to short plant maturity cycle, medium plant height, large open or semi-compact panicle, big and white grain, and adaptation to local growing conditions. The results showed that the sorghum cropping system is dominated by male farmers who mainly grow local landraces. These results will provide updated recommendations for the breeding products profile to meet end-user preferences in Senegal.

Insights into BAY 60-2770 activation and S-nitrosylation-dependent desensitization of soluble guanylyl cyclase via crystal structures of homologous nostoc H-NOX domain complexes.

The soluble guanylyl cyclase (sGC) is an important receptor for nitric oxide (NO). Nitric oxide activates sGC several hundred fold to generate cGMP from GTP. Because of sGC's salutary roles in cardiovascular physiology, it has received substantial attention as a drug target. The heme domain of sGC is key to its regulation as it not only contains the NO activation site but also harbors sites for NO-independent sGC activators as well an S-nitrosylation site (ß1 C122) involved in desensitization. Here we report the crystal structure of the activator BAY 60-2770 bound to the Nostoc H-NOX domain that is homologous to sGC. The structure reveals that BAY 60-2770 has displaced the heme and acts as a heme mimetic via carboxylate-mediated interactions with the conserved YxSxR motif as well as hydrophobic interactions. Comparisons with the previously determined BAY 58-2667 bound structure reveal that BAY 60-2770 is more ordered in its hydrophobic tail region. sGC activity assays demonstrate that BAY 60-2770 has about 10% higher fold maximal stimulation compared to BAY 58-2667. S-Nitrosylation of the BAY 60-2770 substituted Nostoc H-NOX domain causes subtle changes in the vicinity of the S-nitrosylated C122 residue. These shifts could impact the adjacent YxSxR motif and αF helix and as such potentially inhibit either heme incorporation or NO-activation of sGC and thus provide a structural basis for desensitization.

Structure of cinaciguat (BAY 58-2667) bound to Nostoc H-NOX domain reveals insights into heme-mimetic activation of the soluble guanylyl cyclase.

Heme is a vital molecule for all life forms with heme being capable of assisting in catalysis, binding ligands, and undergoing redox changes. Heme-related dysfunction can lead to cardiovascular diseases with the oxidation of the heme of soluble guanylyl cyclase (sGC) critically implicated in some of these cardiovascular diseases. sGC, the main nitric oxide (NO) receptor, stimulates second messenger cGMP production, whereas reactive oxygen species are known to scavenge NO and oxidize/inactivate the heme leading to sGC degradation. This vulnerability of NO-heme signaling to oxidative stress led to the discovery of an NO-independent activator of sGC, cinaciguat (BAY 58-2667), which is a candidate drug in clinical trials to treat acute decompensated heart failure. Here, we present crystallographic and mutagenesis data that reveal the mode of action of BAY 58-2667. The 2.3-A resolution structure of BAY 58-2667 bound to a heme NO and oxygen binding domain (H-NOX) from Nostoc homologous to that of sGC reveals that the trifurcated BAY 58-2667 molecule has displaced the heme and acts as a heme mimetic. Carboxylate groups of BAY 58-2667 make interactions similar to the heme-propionate groups, whereas its hydrophobic phenyl ring linker folds up within the heme cavity in a planar-like fashion. BAY 58-2667 binding causes a rotation of the alphaF helix away from the heme pocket, as this helix is normally held in place via the inhibitory His(105)-heme covalent bond. The structure provides insights into how BAY 58-2667 binds and activates sGC to rescue heme-NO dysfunction in cardiovascular diseases.

Is Nostoc H-NOX a NO sensor or redox switch?

Nostoc sp. (Ns) H-NOX is a heme protein found in symbiotic cyanobacteria, which has approximately 35% sequence identity and high structural homology to the beta subunit of soluble guanylyl cyclase (sGC), suggesting a NO sensing function. However, UV-vis, EPR, NIR MCD, and ligand binding experiments with ferrous and ferric Ns H-NOX indicate significant functional differences between Ns H-NOX and sGC. (1) After NO binding to sGC, the proximal histidine dissociates from the heme iron, causing a conformational change that triggers activation of sGC. In contrast, formation of pentacoordinate (5c) NO heme occurs to only a limited extent in Ns H-NOX, even at >1 mM NO. (2) Unlike sGC, two different hexacoordinate (6c) NO complexes are formed in Ns H-NOX with initial and final absorbance peaks at 418 and 414 nm, and the conversion rate is linearly dependent on [NO], indicating that a second NO binds transiently to catalyze formation of the 414 nm species. (3) sGC is insensitive to oxygen, and ferric sGC prepared by ferricyanide oxidation has a 5c high-spin heme complex. In contrast, Ns H-NOX autoxidizes in 24 h if exposed to air and forms a 6c ferric heme complex, indicating a major conformational change after oxidation and coordination by a second histidine side chain. Such a large conformational transition suggests that Ns H-NOX could function as either a redox or a NO sensor in the cyanobacterium.

Long-term outcome of phase II trial evaluating chemotherapy, chemoradiotherapy, and surgery for locoregionally advanced esophageal cancer.

PURPOSE: To evaluate the long-term outcome of chemotherapy, chemoradiotherapy, and surgery for patients with locoregionally advanced esophageal cancer. METHODS AND MATERIALS: Thirty-eight patients with locoregionally advanced esophageal cancer were entered into a Phase II study between November 1996 and October 1998 at the University of Texas M. D. Anderson Cancer Center. Patients initially received two cycles of chemotherapy with paclitaxel (200 mg/m(2)), 5-fluorouracil (750 mg/m(2)/d for 5 days), and cisplatin (15 mg/m(2)/d for 5 days), followed by chemoradiotherapy, consisting of radiation (45 Gy during 5 weeks) with 5-fluorouracil (300 mg/m(2)/d during radiation) and cisplatin (15 mg/m(2)/d for 5 days). Surgical resection was performed 4-6 weeks after the completion of the chemoradiotherapy. RESULTS: Most patients had adenocarcinoma (n = 32; 84%). Pretreatment endoscopic ultrasonography revealed T3 tumors in 33 patients (87%) and N1 disease in 25 patients (66%). Thirty-seven patients (97%) completed the planned chemotherapy and chemoradiotherapy, and 35 patients (92%) underwent surgery, with a 30-day mortality rate of 6% (2 of 35 patients). A pathologic complete response or microscopic residual carcinoma (<10% viable) was found in 25 (71%) of 35 patients and was associated with a disease-free survival rate of 72% at 3 years and 51% at 5 years. On the basis of an intention-to-treat analysis and a median potential follow-up of 58 months, the 3- and 5-year overall survival rate for all 38 patients was 63% and 39%, respectively. CONCLUSION: The long-term results of this study suggest that the strategy of induction chemotherapy followed by chemoradiotherapy and surgery is safe and warrants further evaluation in the treatment of patients with locoregionally advanced esophageal cancer.

Treatment outcomes of resected esophageal cancer.

OBJECTIVE: To assess the evolution of treatment and outcome for resected esophageal cancer at a single institution. SUMMARY BACKGROUND DATA: Strategies for optimizing the treatment of resected esophageal cancer continue to evolve over time. The outcomes of these evolving treatments in the context of improved diagnostic staging and changing epidemiology have not been carefully analyzed in a single institution. METHODS: One thousand ninety-seven consecutive patients with primary esophageal cancer underwent surgery during the period 1970 to 2001. Nine hundred ninety-four patients underwent curative esophagectomy and were analyzed for changing demographics. Eight hundred seventy-nine patients who did not have systemic metastases and survived the perioperative period were assessed by multivariate analysis for factors associated with long-term survival. RESULTS: During the study period the overall median survival increased from 17 to 34 months, and combined hospital and 30-day mortality decreased from 12% to 6%. The R0 resection rate increased from 78 to 94%, and adenocarcinoma replaced squamous cell carcinoma as the predominant histology (83% vs. 17%). No change in survival with time was noted for patients treated with surgery alone having the same postoperative pathologic stage (pTNM). An increased proportion of patients had preoperative chemoradiation in the last 4 years of the study (59% vs. 2%). Preoperative chemoradiation was associated with a longer survival and increased likelihood of achieving a complete resection. Multivariate analysis showed that long-term survival was associated with a complete resection and the preoperative staging strategy used, while the use of preoperative chemoradiation was the most significant factor associated with ability to achieve an R0 esophageal resection. CONCLUSIONS: This study shows favorable trends in the survival of patients with resected esophageal cancer over time. The increased use of preoperative chemoradiation, better preoperative staging, and other time-dependent factors may have contributed to the observed increase in survival.