Pattern of expression of cyclin T1 in human tissues.

Cyclin T1 was recently identified, together with cdk9 (previously named PITALRE), as part of the TAK multiprotein complex, a co-factor targeted by the human immunodeficiency virus Type 1 (HIV-1) protein named Tat, suggesting a role for this complex in transcription elongation. Although studies on mRNA and protein expression have shown that cyclin T1 is ubiquitous in adult human tissues, no data have yet been reported regarding the expression of this protein in different cell lineages. Using a polyclonal antiserum raised against cyclin T1, we investigated the pattern of expression of this protein in adult human tissues by immunohistochemistry. Cyclin T1 was expressed ubiquitously, although different levels of expression were found in various organs. Some specialized tissues, such as blood, lymphoid tissues, and cells of connective tissue origin, showed high cyclin T1 expression. These specific expression patterns are only partially justified by some well-known specialized functions of cyclin T1 in certain cell types, such as its involvement in peripheral blood lymphocytes and monocyte differentiation. The high expression level found in other tissues suggests new possible roles for cyclin T1 in cell types other than those of lymphoid tissue.