Assessment of oestrogen receptor mRNA size in breast cancer
Total RMA from 46 breast tumours was qualitatively and quantitatively analyzed by hybridization with an ER-α full-length probe (Northern blotting). All tumours expressed a full-length 6.6-kb ER mRNA (small-sized species were not recorded). Moreover, a good correlation was obtained when the amount of 6.6-kb ER mRNA estimated by densitometry was compared with corresponding [3H]oestradiol-binding capacities (DCC values; Fig. 4). Hence, ER isoforms of low molecular weight did not appear to be encoded by truncated ER mRNAs, suggesting that they were generated by proteolysis. Whether such a phenomenon is an intracellular process is analyzed below.