A study on epidermal growth factor receptors in human colorectal cancer

112

Abstracts from the l l th International Symposium on Regulatory Peptides

A STUTY ON EPIDERMAL GROWTH FACTOR RECEPTORS IN HUMAN COLORECTAL CANCER. GM

Liu, RL

Jiang. Department of Digestive

Disease, The

First Clinical

College, China Medical University. Shenyang 110001P.R. China. Epidermal growth 21 resected

factor receptor (EGFR) binding assay was performed in

colorectal cancer tissures by

using

radioligan

receptor

assay and the same number of colorectal non-cancer tissures as controls. Membrane extracts of colorectal cancer cells and colorectal prepared for binding with 12~I-EGF. It was found 1 mg

membrane

protein

was

The difference

control was significant (p
binding of 12SI-EGF in cancer

that of

control (38.07 _+4. 75 fmol The

that 12SI-EGF bound in

20. 16_+4.76 fmol and 11.22_+2.96

cancers and controls respectively.

protein, p
vs

was

vs

and

EGF

and

that

the

higher than

fmol/mg

membrane

cancer was greater

1. 34_+0. 40 nmol/L ), but

there was no significant statistical difference between them. of colorectal cancer

fmol in

cancer

showed

significantly

29. 31 _+1. 64

than that of control ( i. 31_+0. 33 nmoliL

between

analysis

affinity of EGFR, KD, in

The results suggest that E G F R

cells were

(P>O. 05).

was over-expressed in the cell membrane may play an important role in the

au-

tocrine/paracrine regulatory mechanism of the colorectal cancer.

AMYLIN INHIBITS GLYCOGEN SYNTHASE ACTIVITY AND GLUCOSE UPTAKE IN L6 RAT MYOBLASTS AT PHYSIOLOGICAL CONCENTRATIONS. J Liu, TE Adrian. Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE. We have previously reported increased plasma levels ofamylin (islet amyloid polypeptide) as well as a decrease in skeletal muscle glycogen synthase activity in pancreatic cancer patients with diabetes. To investigate the possible role ofamylin in inducing peripheral insulin resistance in pancreatic cancer, we studied the effect of rat amylin on insulin-stimulated glycogen synthase in L6 myoblasts. The effect of amylin on glucose uptake was also studied in GLUT-4 gene transfected rat L6 myoblasts which were more sensitive to insulin stimulation. Total glycogen synthase activity measured in the presence of 10 mM glucose 6-phosphate (G-6-P) was not affected by incubation with 100 nM insulin. However, glycogen synthase I activity, which was measured in the presence of 0.1 mM G-6-P, was increased from basal of 89.4+6.5 nmol/min/mg protein to 114.4+6.2 with 100 nM insulin (P<0.05). Rat amylin (10 pM to 100 nM) significantly reduced insulin-stimulated glycogen synthase I activity to 94.1±4.0 (P<0.05). The fractional velocity of glycogen synthase activity, which was increased from 16.6% in the basal to 22.1% with 100 nM insulin (P<0.05), was significantly decreased to 18.6% in the presence of 10 pM amylin (P<0.05). Rat amylin also had a small but significant inhibitory effect on basal glycogen synthase I activity as well as on fractional velocity. Rat amylin (10 pM-100 nM, significantly inhibited glucose uptake stimulated by 100 nM insulin in GLUT-4 transfected L6 cells. At the lowest concentration of amylin (10 pM) tested, insulin-stimulated glucose uptake was reduced from 134% to only 49% above the basal level (P<0.05). Rat amylin had no significant effect on basal glucose uptake in these cells. Since the mean fasting plasma amylin concentration in both rat and human is about 10 pM, these findings show that this peptide can inhibit insulin-stimulatedglucose metabolism in skeletal muscle cells within its physiological concentration range. Further studies are needed to identify the receptor-mediated mechanism responsible for these effects on skeletal muscle. Furthermore, amyliin may play a role in the prof~,md peripheral insulin resistance in pancreatic cancer.