Nuclear and cytoplasmic distribution of cellular myb protein in human haematopoietic cells evidenced by monoclonal antibody.

A monoclonal antibody was used for analysing the expression of the cellular myb (c-myb) protein in a variety of established human tumor cell lines and its decrease after induction of differentiation. Differentiated resting human T-cells and B-cells do not express detectable amounts of c-myb protein. However, upon mitogenic stimulation in vitro T-cells exhibit strong expression of the c-myb protein as demonstrated by immunocytochemical staining and indirect immunoprecipitation. In contrast to the transformed T-lymphoblastic cell line Molt-4, where c-myb protein is a nuclear antigen, it was found in proliferating normal T-cells almost exclusively distributed in the cytoplasm. Screening of a total of 70 fresh human malignant lymphomas by immunohistochemical staining indicates the presence of the c-myb protein primarily in non-Hodgkin's lymphomas with a large growth fraction, i.e. precursor cell-derived lymphoblastic lymphomas of B-cell type and T-cell type (9/10, 3/4, respectively) and anaplastic large cell Ki-1 lymphomas (5/9), which originate from activated lymphoid cells. The c-myb protein was located predominantly in the nucleus and in some cases additionally in the cytoplasm. The different subcellular locations suggest a dual functional role. While nuclear localisation is exhibited by transformed haematopoietic cells, cytoplasmic localisation appears to be characteristic for proliferating normal T-cells and points to a second property of the c-myb protein other than interaction with DNA.