MICROFILAMENT BUNDLES IN TRANSFORMED MOUSE CLIDX-TRANSFORMED CHO CELL HYBRIDS - CORRELATION WITH TUMORIGENICITY IN NUDE-MICE

Tumorigenic mouse CLID cells (TK-1, thymidine kinase) having a 'crossed' pattern of microfilament bundles were fused by means of polyethylene glycol (PEG) with low tumorigenic** ** The original CHO cells do not produce tumors in nude mice when 106 cells are inoculated per mouse. These cells, however, have been reported to produce tumors when injected into Chinese hamsters. We define a cell line as having a low tumorigenicity if less than 15% of the animals produce tumors when 106 cells are injected. transformed Chinese hamster ovary cells (CHO) (HGPRT-) displaying a normal distribution of microfilament bundles. Eight independent hybrid clones were isolated by selection in HAT media and were studied for their karyotype, pattern of microfilament bundles and tumorigenicity in nude mice. Fluorescent staining of metaphase chromosomes with Hoechst 33258 confirmed with one exception the hybrid character of the clones and further showed that all these hybrids have segregated CHO chromosomes. Indirect immunofluorescence studies using human actin antibodies revealed the 'crossed' pattern of microfilament bundles in all hybrids apart from one (no. 12) which presented a pattern similar to that observed in the CHO parent. Subcutaneous injection of the hybrid clones into nude mice showed that only four were consistently tumorigenic when 106 cells were inoculated per mouse although the period between inoculation and appearance of a small palpable tumour (latent period) was considerably longer (ranging from 24 to 45 days) than that observed in animals inoculated with the parental CLID cells (10 days). Three other hybrids produced tumours in 16 and 33% of the animals whilst Hy 12 failed to produce any tumors at all after 4 months of inoculation. The results clearly showed that no direct relationship could be drawn between the presence of a 'crossed' pattern of microfilament bundles and tumorigenicity in the nude mice. As with our previous studies on non-virally transformed cells, these results indicate that an alteration or loss of microfilament bundles cannot be used as a general assay to assess tumorigenicity at the cellular level. © 1979.