Reed-Sternberg Cells in Hodgkin’s Cell Lines HDLM, L-428, and KM-H2 Are not Actively Replicating: Lack of Bromodeoxyuridine Uptake by Multinuclear Cells in Culture

Abstract

We compared the proliferation of mononuclear and multinuclear cells in four Hodgkin's cell lines, HDLM-1, HDLM-1d, L-428, and KM-H2, by examining their capacity to incorporate bromodeoxyuridine (BrdUrd) into nuclei. Approximately 5% of all cells in HDLM-1 cultures had two or more nuclei, a characteristic of Reed-Sternberg (RS) cells. Unlike mononuclear Hodgkin's (H) cells, these RS cells exhibited no uptake, or only minimal uptake of BrdUrd, suggesting that they did not replicate actively. Cytogenetic study showed that 25% of the HDLM-1 cells contained a tetraploid (4X) set of chromosomes with a characteristic two-peak distribution. Following treatment of HDLM-1 cells with phorbol ester, the percentages of 4X cells and RS cells increased to 50% and 12%, respectively. This increase in RS cells was not likely to be due to cell fusion as shown by the absence of hybridization of BrdUrd-positive and -negative nuclei. Phorbol ester has a short-term effect of blocking the exit of cells from G1 into S phase, but no effect on the transition from S phase to G2/M phase. The block is more prominent in 2X cells than in 4X cells, which may explain the increase in percentage of 4X cells in phorbol ester-treated cultures. In addition, phorbol ester induced the differentiation of H-RS cells, which was accompanied by loss of the marker HeFi-1 from the cell surface. Approximately one third of the RS cells did not express HeFi-1, or expressed only minimal amounts. The findings led us to the following conclusions: (1) The 4X cells probably are formed from 2X H cells as a result of disturbed cytokinesis, but not a cell fusion. (2) A considerable number of 4X cells were H cells, because the number of 4X cells consistently exceeded that of RS cells. (3) Since mitotic figures are extremely rare in RS cells and these cells did not show active BrdUrd uptake, the increased number of RS cells must also be a consequence of disturbed cytokinesis of H cells or a result of nuclear transformation (twisting, convolution, or separation of the nucleus) in H cells. (4) Most RS cells lose their proliferating capacity and some RS cells may undergo further differentiation. Uptake of BrdUrd and phorbol ester induction were also studied on the other three H-RS cell lines, HDLM-1d, L-428, and KM-H2, with results similar to those for HDLM-1.