Nerve growth factor nonresponsive pheochromocytoma cells: altered internalization results in signaling dysfunction.

Variant rat pheochromocytoma (PC12) cells which fail to respond to nerve growth factor (NGF) (PC12nnr5) (Green, S. H., R. E. Rydel, J. L. Connoly, and L. A. Greene. 1986. J. Cell Biol. 102:830-843) bind NGF at both high and low affinity sites. Although still undefined at the molecular level, these have been referred to as type I (high) and type II (low) receptors. They are apparently composed of two membrane-bound proteins, p75 and the protooncogene trk, both of which bind NGF, and apparently contribute singularly or in concert to the two observed affinities, and to the promotion of the NGF effects. In native PC12 cells, only the high affinity receptors are apparently capable of mediating internalization and degradation. PC12nnr5 cells also display type I binding, but the subsequent internalization is not the same fashion as in the parental cell line, nor is it subjected to lysosomal degradation. Rather it is initially sequestered during the first 15 min, and is eventually released intact into the medium. In contrast, EGF is bound, internalized, and degraded by PC12nnr5 cells, albeit less efficiently than in the parent cells. These observations argue that the defect(s) preventing the PC12nnr5 variants from responding to NGF prevents competent internalization, which in the case of NGF, may be required for the full expression of activity. The absence of trk, as one alteration in PC12nnr5 cells (Loeb, D. M., J. Maragos, D. Martin-Zanca, M. V. Chao, L. F. Parada, and L. A. Greene. 1991. Cell. 66:961-966), is consistent with this conclusion

Sequence and expression of the Cc gene, a member of the dopa decarboxylase gene cluster of Drosophila: possible translational regulation.

A transcript has been localized proximal to the dopa decarboxylase (Ddc) gene within a cluster of genes involved in cuticle formation and catecholamine metabolism in Drosophila. This gene, which has been identified as I(2)37Cc, maps 2.0kb from the 5' end of the Ddc gene and is transcribed in the same direction as Ddc. We describe a new deficiency which in conjunction with previous deficiencies localizes the I(2)37Cb and I(2)37Cc loci to the cytogenetic interval 5' to Ddc. We present the sequence of the Cc gene and corresponding cDNA. The Cc message contains several open reading frames 5' to the large open reading frame responsible for the lethal complementation group, suggesting that expression of Cc function may be regulated translationally. The Cc transcript is expressed in early embryos, late embryos, late third instar larvae and adults. We discuss the implications of these findings with respect to the gene organization in the region

Sequence and structure of the dopa decarboxylase gene of Drosophila: evidence for novel RNA splicing variants.

In Drosophila, dopa decarboxylase (DDC) serves a dual role in neurotransmitter production and sclerotization of the cuticle. The Ddc gene is under complex hormonal and tissue-specific control and several sizes of Ddc RNA are observed at embryonic hatching, pupariation and adult eclosion. We present here the complete nucleotide sequence of the Drosophila dopa decarboxylase gene and the partial sequence of two corresponding Ddc cDNAs. The sequence allows us to account for the detailed structure of four of the five major Ddc RNA species observed. The cDNA sequence reveals the existence of previously undetected splicing events and provides evidence for two RNA splicing alternatives which appear to encode two protein isoforms. The structure, processing and developmental regulation of the Ddc transcripts and putative protein isoforms are discussed. Interestingly, the pyridoxal-binding peptide of porcine DDC matches the Drosophila sequence perfectly suggesting considerable selective pressure on at least portions of the sequence. This is the first available Ddc gene sequence from any organism and should serve as a basis of comparison for the related proteins of other species