COORDINATE EXPRESSION AND PROLIFERATIVE ROLE OF HOXB GENES IN ACTIVATED ADULT T-LYMPHOCYTES

We investigated the expression of HOXB cluster genes in purified phyto hemagglutinin (PHA)-activated T lymphocytes from normal adult peripher al blood by reverse transcription PCR and RNase protection. These gene s are not expressed in quiescent T cells, except for barely detectable BI RNA. After the PHA stimulus, HOXB gene activation initiates coordi nately as a rapid induction wave in the 3'--> 5' cluster direction (i. e., from HOXB1 through B9 genes). Thus, (i) expression of the foremost S'-located BI and B2 genes peaks 10 min after PKA addition and then r apidly declines, (ii) activation of B3, B4, and B5 begins 10 min after PHA addition and peaks at later times i.e., at 120 min for B5), (iii) B6, B7, and B9 are expressed at a low level starting at later times ( 45 to 60 min), and (iv) B8 remains silent. Treatment of PHA-activated T lymphocytes with antisense oligonucleotides to B2 or B4 mRNA causes a drastic inhibition of T-cell proliferation and a decreased expressio n of T-cell activation markers (i.e., interleukin 2 and transferrin re ceptors). Similarly, treatment of CEM-CCRF, Peer, and SEZ627 T acute l ymphocytic leukemia cell lines with anti-B4 oligomer markedly inhibits cell proliferation. Finally, T cells stimulated by a low dosage of PH A in the presence of 1 mu M retinoic acid show a marked increase of bo th HOXB expression, particularly B2, and cell proliferation. These stu dies provide novel evidence on the role of HOX genes in adult cell pro liferation. (i) Coordinate, early activation of HOXB genes from the 3' --> 5' cluster side apparently underlies T-cell activation. (ii) The e xpression pattern in adult PHA-activated T cells is strikingly similar to that observed in retinoic acid-induced teratocarcinoma cells (A. S imeone, D. Acampora, L. Arcioni, P. W. Andres, E. Boncinelli, and F. M avilio, Nature (London) 346:763-766, 1990), thus suggesting that molec ular mechanisms underlying HOX gene expression in the earliest stages of development may also operate in activated adult T lymphocytes.