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Materials and Methods

Reverse Transcription–PCR. Poly (A) RNA was isolated from tissue or cultured cells by homogenization in Trizol (Life Technologies, Grand Island, NY) followed by selection on Oligotex columns (Qiagen, Chatsworth, CA). Twenty nanograms of polyA RNA were reverse transcribed with an oligo (dT) primer in 50 mM TrisCl75 mM KCl3 mM MgCl2 0.01 M DTT20 units of RNase inhibitor0. 5 mM dNTP by using 200 units of Superscript II (Life Technologies), then treated with 1 unit of RNase H. PCR amplification (94 C for 2 min; 35 cycles of 94 C for 30 s, 60 C for 30 s, 72 C for 1 min; 72 C for 2 min) was conducted in 20 mM TrisCl50 mM KCl1. 5 mM MgCl2 0.2 mM dNTP0. 4 μM primer pairs, using 1.25 units of platinum Taq (Life Technologies) and the following primers: VR-1, 5-caaggctgtcttcatcatcc-3 and 5-attcccacacacctcccagttc-3; VRL-1, 5-gatgaagagggcaatgc-3, 5-ccattcagtctccatgaagc-3 …