Regulation of GP63 mRNA stability in promastigotes of virulent and attenuated Leishmania chagasi

GP63 is a 63-kDa glycoprotein that is abundantly expressed on the surface o f all Leishmania species and is involved in several steps of promastigote i nfection of host cells. Leishmania chagasi has at least 18 haploid nsp (maj or surface protease) genes encoding GP63 that are divided into three classe s, mspS, mspL or mspC, according to their unique 3' UTR sequences and diffe rential expression. All three msp classes are constitutively transcribed du ring Virulent promastigote growth in vitro, although mspL mRNA is most abun dant during logarithmic phase and mspS mRNA predominates in stationary phas e. Thus, the steady state levels of the mspL and mspS mRNAs are post-transc riptionally regulated. Using Actinomycin D to arrest transcription, we foun d that in Virulent promastigotes the half-life (t(1/2)) Of mspL mRNA is coo rdinately modulated with growth phase, decreasing from a mean of 84 min dur ing early logarithmic growth to a mean of 17 min at a stage intermediate be tween logarithmic and stationary phase. However, in attenuated promastigote s, the t(1/2) of mspL RNA remains the same throughout parasite growth. In c ontrast to mspL RNA, the t(1/2) of mspS and mspC RNA is constant throughout all growth phases of both virulent and attenuated promastigote growth. The presence of the translation inhibitor cycloheximide increases the t(1/2) o f mspL RNA 4-6-fold in both Virulent and attenuated promastigotes at all gr owth phases. These results indicate that the t(1/2) of mspL RNA is maintain ed by at least two distinct mechanisms - one activated during growth to sta tionary phase and the other dependent on a labile negative regulatory prote in factor(s). (C) 2001 Elsevier Science B.V. All rights reserved.