The identification of the inhibitory gamma-subunits of the type 6 retinal cyclic guanosine monophosphate phosphodiesterase in non-retinal tissues: differential processing of mRNA transcripts.

Here, we report that mouse lung expresses gamma-subunit (PDEgamma) transcripts of the rod and cone photoreceptor cGMP phosphodiesterase genes (Pde6g and Pde6h, respectively). Moreover, a major 14-kDa protein (p14) in lung membranes was immunostained with antibodies that react with both rod and cone PDEgamma. We show that p14 is, in fact, a mixture of rod and cone PDEgamma, based on three additional lines of evidence. First, p14 was also immunostained with antibodies specific for the cone PDEgamma isoform. Second, the expression of p14 immunostained with antibodies recognizing both rod and cone PDEgamma was substantially reduced in lung membranes from Pde6g-/- mice. In contrast, the fraction of p14 stained with cone PDEgamma-specific antibodies was not altered in the Pde6g-/- mice. Third, the absence of the Pde6g transcript was correlated with reduced levels of p14 in Pde6g-/- mice. We have also found that mouse lung contains a small Pde6h transcript that has a 41-bp deletion resulting in a frame change, derived by differential mRNA processing of exon 3 of Pde6h. BLAST searches also revealed a rat ovary EST that has the same 41-bp deletion causing the same frame change. However, the premature in-frame stop codon seen in the short Pde6h transcript is absent and the regular stop codon is out of frame leading to a predicted ORF extension into the 3' UTR. These findings show that rod and cone PDEgamma isoforms are expressed in lung and seem to have a critical role in regulating p42/p44 mitogen-activated protein kinase signaling.