Characterization of high affinity neurotensin receptor NTR1 in HL-60 cells and its down regulation during granulocytic differentiation

1 We investigated responses to neurotensin in human promyelocytic leukaemia HL-60 cells. 2 Neurotensin increased the cytosolic calcium concentration ([Ca2+](i)) in a concentration-dependent manner and also produced inositol 1,4,5-trisphosphate (InsP(3)). 3 Among the tested neurotensin analogues, neurotensin 8-13, neuromedin-N, and xenopsin also increased [Ca2+](i), whereas neurotensin 1-11 and neurotensin 1-8 did not elicit detectable responses. 4 SR48692, an antagonist of NTR1 neurotensin receptors, blocked the neurotensin-induced [Ca2+](i) increase, whereas levocabastine, which is known as an NTR2 neurotensin receptor antagonist, did not attenuate the neurotensin-evoked effect. 5 The expression of NTR1 neurotensin receptors was confirmed by Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). 6 During 1.25% dimethylsulfoxide (DMSO)-triggered granulocytic differentiation of HL-60 cells, the neurotensin-induced [Ca2+](i) rise became gradually smaller and completely disappeared 4 days after treatment with DMSO. The mRNA level for neurotensin receptors was also decreased after differentiation. 7 The results show that HL-60 cells express NTR1 neurotensin receptors and suggest that granulocytic differentiation involves transcriptional regulation of the receptors resulting in down-regulation of the neurotensin-induced signalling.