Kappa receptors cloning

Prodynorphin contains three copies of Leu-enkephalin with carboxy-termi-nus extended polypeptides of various lengths known as dynorphin A (or dynorphin 1-17), dynorphin B (dynorphin 1-13), or a- and 3-neoendorphin. These peptides derived from prodynorphin are selective to kappa receptors and can also be further broken down to Leu-enkephalin. The identification of the delta receptor (or the enkephalin receptor) was a direct consequence of the discovery of enkephalins. This chapter will review the major events that are important for the identification of delta receptors and the subsequent cloning of delta receptor genes, and eventually all other opioid receptor genes. 

The cloning of the delta receptor set in motion a competitive race to identify other members of the opioid receptor family. Homologous orphan clones were quickly assessed for opioid receptor binding properties, which resulted in the identification of the kappa receptor and reassignment of an orphan clone as the delta opioid receptor [31]. PCR, genomic, and cDNA screens revealed the mu opioid receptor and an extremely abundant orphan member, named opioid receptor-like (ORL-1) receptor (reviewed by Massotte and Kieffer [30]). 

Binding and Activity of Opioid Ligands at the Cloned Human Delta, Mu, and Kappa Receptors... 

Nishi M., Takeshima H., Fukada K., Kato S., Mori K. cDNA cloning and pharmacological characterization of an opioid receptor with high affinities for kappa-subtype selective ligands. FEBS Lett. 330 77, 1993. 

Raynor K., Kong H., Chen Y. et al. Pharmacological characterization of the cloned kappa-, delta-, and mu-opioid receptors. Mol. Pharmacol. 45 330, 1993. 

Raynor K, Kong H, Chen Y, Yasuda K, Yu L, Bell GI, Reisine T. Pharmacological characterization of cloned kappa, delta and mu opioid receptors. Mol Pharmacol 1994 45 330-334. 

Tallent M, Dichter M, Bell GI, Reisine T. The cloned kappa opioid receptor couples to an N-type Ca++ current in undifferentiated PC 12 cells. Neuroscience 1994 63 1033-1040. 

Tallent M, Dichter M. Reisine T. Coupling of the cloned kappa and mu opioid receptors to cellular effector systems is differentially regulated. Neuroscience 1998 85 873-885. 

Progress in the molecular characterization of opioid receptors has been slower than for other cell-surface receptors and, to date, none has been sequenced or cloned and the second messengers mediating opioid actions are still unknown. The literature in this area has been reviewed in 1990 by Lo and Smith [11], who cite three main problems with the opioid receptor it is difficult to solubilize, there are no simple biochemical assays to test the functional integrity of an isolated receptor extract and there are at least three receptor subtypes (designated as mu, kappa and delta). 

Yasuda K, Raynor K, Kong H, et al. Cloning and functional comparison of kappa and delta opioid receptors from mouse brain. Proc Natl Acad Sci USA 1993 90 6736-6740. 

Recently, Sedqi et al. [24] were able to clone a delta opioid receptor complementary DNA by expression of cDNA library from activated thymocytes in Cos 7 cells, whose amino acid sequence was similar to the neural counterpart. Interestingly, they also observed that transcripts for kappa and mu opioid receptors were not detected in thymocytes. Furthermore, Gave-riaux et al. [25] demonstrated transcripts for the delta opioid receptor in T-lymphocyte, B-lymphocyte, and monocyte cell lines, as well as in murine splenocytes. However, they observed that the kappa opioid receptor transcript was only found in B-cell lines. These studies may suggest a selective expression of the delta opioid receptor in specific cells and tissues of the immune system and suggests specialized functions in different anatomical regions. 

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