QUANTITATIVE-ANALYSIS BY POLYMERASE CHAIN-REACTION OF GROWTH-HORMONE RECEPTOR GENE-EXPRESSION IN HUMAN LIVER AND MUSCLE

A single form of GH receptor (GHR) messenger RNA (mRNA) of 4.5 kilobases, encoding the full-length GHR, has been found in man. To measure the absolute number of mRNA molecules encoding the GHR in human tissues, we developed a quantitative polymerase chain reaction assay. An internal control RNA was constructed by inserting a 50-basepair fragment of the rat PRL receptor complementary DNA into a portion of the human GHR complementary DNA. The internal control RNA and the target mRNA were amplified together with the same set of primers. Twenty-four cycles of amplification were used to satisfy an exponential phase of amplification. It was possible to detect as few as 500 molecules of target mRNA/mu g total RNA. In 3 liver samples obtained from normal donors at the time of transplant, the amount of GHR mRNA ranged from 0.5 +/- 0.1 to 1.4 +/- 0.4 x 10(6) molecules/mu g total RNA. These results were confirmed by slot blot analysis of the same samples. The number of receptor transcripts did not appear to be correlated with the receptor-binding capacity found in the 3 liver samples. In 7 muscle biopsies, GK receptor mRNA varied between 4.0 +/- 0.4 and 34.6 +/- 1.4 x 10(4) molecules/mu g total RNA. This technique allows direct measurement of GHR gene expression in human tissues and represents a valuable tool, particularly for tissues such as muscle, in which the receptor protein cannot be measured using conventional binding assays.