Various heterotrimeric guanine nucleotide-binding proteins have been identified on the basis of the individual subtypes of their alpha subunits. The beta gamma complexes, composed of beta and gamma subunits, remain tightly associated under physiological conditions and have been assumed to constitute a common pool shared among various guanosine triphosphate (GTP)-binding (G) protein heterotrimers. Particular alpha and beta subunit subtypes participate in the signal transduction processes between somatostatin or muscarinic receptors and the voltage-sensitive L-type calcium channel in rat pituitary GH3 cells. Among gamma subunits the gamma 3 subtype was found to be required for coupling of the somatostatin receptor to voltage-sensitive calcium channels, whereas the gamma 4 subtype was found to be required for coupling of the muscarinic receptor to those channels.

Regulatory GTP-binding proteins (G proteins) are membrane-attached heterotrimers (alpha, beta, gamma) that mediate cellular responses to a wide variety of extracellular stimuli. They undergo a cycle of guanine-nucleotide exchange and GTP hydrolysis, during which they dissociate into alpha-subunit and beta gamma complex. The roles of G-protein alpha-subunits in these processes and for the specificity of signal transduction are largely established; the beta- and gamma-subunits are essential for receptor-induced G-protein activation and seem to be less diverse and less specific. Although the complementary DNAs for several beta-subunits have been cloned, isolated subunits have only been studied as beta gamma complexes. Functional differences have been ascribed to the gamma-subunit on the basis of extensive sequence similarity among beta-subunits and apparent heterogeneity in gamma-subunit sequences. Beta gamma complexes can interact directly or indirectly with different effectors. They seem to be interchangeable in their interaction with pertussis toxin-sensitive alpha-subunits, so we tested this by microinjecting antisense oligonucleotides into nuclei of a rat pituitary cell line to suppress the synthesis of individual beta-subunits selectively. Here we show that two out of four subtypes of beta-subunits tested (beta 1 and beta 3) are selectively involved in the signal transduction cascades from muscarinic M4 (ref. 4) and somatostatin receptors, respectively, to voltage-dependent Ca2+ channels.

Well differentiated neuroendocrine tumors (NETs) of the stomach (gastric carcinoid tumors) are observed more often, with a tenfold increase in the US in the last 30 - 35 years, and the prognosis has improved greatly in that time. Nowadays most carcinoids of the stomach are diagnosed at an early stage. Four types of gastric NETs have been proposed and recognition of the type is important for defining the diagnostic approach and treatment. Often gastric NETs (especially type 1) are found incidentally during a gastroscopy performed for other reasons; most of these NETs are smaller than 20 mm in size. Conservative management and endoscopic surveillance is adequate for well differentiated, multifocal gastric carcinoids (type 1 or type 2 gastric NETs) that are less than 10 - 20 mm in diameter, unless they show angioinvasion, infiltrate the muscular wall, or have a proliferation rate above 2 %. Endoscopic ultrasound is the method of choice to determine tumor size and depth of infiltration. It is essential to distinguish between multifocal (types 1 and 2) and unifocal type 3 or type 4 gastric NETs, since surgery is indicated for type 3 gastric NETs larger than 10 mm in diameter and for poorly differentiated (localized) neuroendocrine gastric carcinomas (type 4 gastric NET). For optimal management, the type, biology, and stage of the tumor as well as the individual situation of the patient must be considered. Most patients with well differentiated gastric NETs can be treated conservatively and be followed up with endoscopic surveillance.

Survivin, a new member of the family of apoptosis inhibitors, is expressed almost exclusively in proliferating cells, above all in cancers. Subcellular localisation and prognostic implications of the survivin protein have not yet been determined in oesophageal squamous cell carcinoma. The survival of 84 patients with oesophageal squamous cell carcinomas was correlated with the extent of immunohistochemical survivin expression in tumour cell nuclei. Tumours were scored positive when 45% cells stained positive. Patients were followed up for at least 5 years or until death. In normal oesophageal squamous cell epithelium, some cytoplasmic survivin expression was detected in the basal cells, whereas proliferating cells showed nuclear staining of survivin. Nuclear expression of survivin was also detected in 67 cancers (80%). The mean survival for patients of this group (28 months, range 20 -36) was significantly less than that for patients without survivin expression in the tumour cell nuclei (108 months, range 62 -154, P ¼ 0.003). Using univariate analysis, nuclear survivin expression (P ¼ 0.003), tumour depth (P ¼ 0.001), lymph node metastasis (P ¼ 0.003) and stage (Po0.001) were the best predictors of survival. In contrast, cytoplasmic survivin staining was noted in 53 (63%) tumours and had no prognostic relevance. In conclusion, the analysis of nuclear survivin expression identifies subgroups in oesophageal squamous cell cancer with favourable (survivin À ) or with poor prognosis (survivin + ). We suggest that the determination of nuclear survivin expression could be used to individualise therapeutic strategies in oesophageal squamous cell cancer in the future.

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