The CDK9-associated cyclins T1 and T2 exert opposite effects on HIV-1 Tat activity.
OBJECTIVE
To examine the functional interaction between HIV-1 Tat protein and the cyclin T1 and T2 proteins which, in association with cyclin dependent kinase (CDK)9, are the regulatory subunits of the TAK/P-TEFb cellular complex strictly required for Tat transactivation.


METHODS
HIV-1 long terminal repeat (LTR) reporter plasmid was co-transfected into human and rodent cells with expression vectors encoding Tat and vectors encoding the cyclins T1, T2a and T2b, respectively.


METHODS
Tat-mediated transactivation of HIV-1 LTR-driven transcription was compared in the presence or absence of different cyclins T (T1, T2a and T2b), upon co-transfections into human and rodent cell lines. Protein interactions were analysed by in vitro binding assays.


RESULTS
It was found that Tat function in rodent cells is enhanced by co-expression of cyclin T1 but not cyclin T2. The N-terminal region (amino acids 1-290) of cyclin T1 is sufficient for this function and for binding to Tat and CDK9. Cyclin T2 binds to CDK9 but not to Tat. Moreover, enforced expression of cyclin T2 inhibits cyclin T1-mediated enhancement of Tat in rodent cells and it represses Tat activity in human cells.


CONCLUSIONS
Efficient Tat transactivation in rodent cells occurs in the presence of human cyclin T1 but not in the presence of cyclin T2; overexpression of cyclin T2 inhibits Tat function in both rodent and human cells.
Napolitano
G
G
Department of Genetics, University of Naples Federico II, and International Institute of Genetics and Biophysics, Italy.
Licciardo
P
P
Gallo
P
P
Majello
B
B
Giordano
A
A
Lania
L
L
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D015696:Gene Products, tat / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism*; D006801:Humans; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D020079:Terminal Repeat Sequences / Q000235:genetics; D014158:Transcription, Genetic; D054322:tat Gene Products, Human Immunodeficiency Virus
C503684:CCNT1 protein, human; D056906:Cyclin T; D016213:Cyclins; D015696:Gene Products, tat; D011994:Recombinant Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases