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The western corn rootworm (WCR, Diabrotica virgifera virgifera) gene, dvssj1, is a putative homolog of the Drosophila melanogaster gene, snakeskin (ssk). This gene encodes a membrane protein associated with the smooth septate junction (SSJ) which is required for the proper barrier function of the epithelial lining of insect intestines. Disruption of DVSSJ integrity by RNAi technique has been shown previously to be an effective approach for corn rootworm control, by apparent suppression of production of DVSSJ1 protein leading to growth inhibition and mortality. To understand the mechanism that leads to the death of WCR larvae by dvssj1 double-stranded RNA, we examined the molecular characteristics associated with SSJ functions during larval development. Dvssj1 dsRNA diet feeding results in dose-dependent suppression of mRNA and protein; this impairs SSJ formation and barrier function of the midgut and results in larval mortality. These findings suggest that the malfunctioning of the SSJ complex in midgut triggered by dvssj1 silencing is the principal cause of WCR death. This study also illustrates that dvssj1 is a midgut-specific gene in WCR and its functions are consistent with biological functions described for ssk.

Proteolytic processing of proenkephalin was examined in several subclones of AtT-20 cells stably transfected with rat proenkephalin cDNA (AT/PE cells). Proenkephalin is synthesized in both N-glycosylated and unglycosylated forms, as demonstrated by treatment with tunicamycin. RIAs and Western blot studies showed that AT/PE clones process proenkephalin at some, but not all, Lys-Arg sequences in a limited processing profile reminiscent of bovine adrenal chromaffin cells. Pulse-chase studies using Met5-enkephalin-Arg-Gly-Leu antiserum demonstrated that 50% of the precursor is processed within 1 h, and processing is complete after 2.5 h with the production of the 5.3-kilodalton (kDa) peptide. Further cleavage to the octapeptide Met5-enkephalin-Arg-Gly-Leu is minimal. Radiosequencing results verified the efficient cleavage of a Lys-Lys site within proenkephalin that resulted in the production of the 5.3-kDa peptide. Proenkephalin cleavage products stored within cells, which included the 5.3-kDa peptide, could be released upon stimulation of cells with BaCl2 (2-fold above basal levels), 8-bromo-cAMP or CRF (7- and 8-fold above basal levels, respectively), and a mixture of BaCl2 and 8-bromo-cAMP (20-fold above basal levels). An important difference between the processing of proenkephalin and the ACTH/endorphin precursor (POMC) in AtT-20 cells is efficient cleavage of a Lys-Lys site in proenkephalin and not in POMC. The ability of AT/PE to process proenkephalin in a natural manner makes it a suitable model system to investigate elements involved in the processing of proenkephalin at Lys-Lys sites.