Molecular and Functional Studies of Inhibitory G Protein in RINm5F Cells

Abstract

Inhibitory G proteins (Gi) play an important role in cell proliferation. In order to characterize Gi proteins in RINm5F (RIN) cells, we first established RIN cells in cell culture. Immunoblot analysis was performed on extracted G proteins using Western blot techniques and a Gi-specific antibody. We identified three prominent bands consistent with three distinct inhibitory alpha subunits of membrane-bound G protein (Gi) in RIN cells. In contrast, we identified only one prominent distinct inhibitory alpha subunit of G protein in an equal quantity of membrane-protein in our control (normal rat pancreas). In several cell types, Gi is known to mediate the inhibitory action of somatostatin on intracellular cyclic AMP (cAMP) accumulation. Therefore, we studied the action of the long-acting analogue of somatostatin, octreotide (SMS), on basal and 3-isobutyl-1-methylxanthine-stimulated cAMP accumulation in RIN cells. SMS did not inhibit cAMP accumulation or tritiated thymidine incorporation into DNA (TTID) in RIN cells. However, when treatment with SMS is supplemented with the nonhydrolyzable analogue of guanine nucleotide, Gpp(NH)p (Gpp), which is known to dissociate G proteins into its constitutive subunits, then SMS+Gpp induced an inhibitory action and significantly reduced cAMP accumulation and TTID. These data are consistent with the concept of qualitatively and functionally altered inhibitory G protein expression in the insulin-producing, islet cell (RINm5F) rat insulinoma tumor cell line. Further study of human tumors will lead to new insights into the clinical implications of G protein-mediated signal transduction in insulinoma.

Mechanisms of galanin‐induced contraction in the rat myometrium

“…Subsequent studies revealed that galanin is widely distributed in the central nervous system, peripheral nerves and several endocrine tissues and that it has a broad spectrum of biological effects, such as hormone and neurotransmitter release, antinociception, change in feeding behavior and smooth muscle contraction or relaxation (Rokaeus, 1987). These biological effects of galanin are mediated by receptors coupled with pertussis toxin‐sensitive guanosine 5′‐triphosphate binding protein (G‐protein) to downstream effector systems, including adenylate cyclase, phospholipase C (PLC) and receptor‐activated ion channels (de Mazancourt et al , 1994; Gillison & Sharp, 1994; McLeod et al, 1994; Valkna et al , 1995). Recently, two subtypes of galanin receptor have been cloned and termed GALR1 and GALR2, respectively (Habert‐Ortoli et al , 1994; Burgevin et al , 1995; Parker et al , 1995; Howard et al , 1997).…”

Feeding and Fluids in the Premature and Sick Newborn in the Low-Middle Income Countries

“…The nutrient deficit occurring in the early weeks post delivery, when the infant is medically fragile, is difficult to overcome. Weight, length and head circumference measurements remain important clinical indicators of growth, but composition of weight gain is emerging as a necessary measure in determining the adequacy of nutrition intake and growth (McLeod et al, 1994). The need to monitor weight for estimation of fluid balance is a different task than monitoring for growth, and the practitioner needs to be aware of both issues.…”