Stimulation of c-jun and c-myb in rat Sertoli cells following exposure to retinoids.

Circulating hormones are engaged in initiating and controlling the process of spermatogenesis, however, the Sertoli cell tight junctions prevent these substances from directly influencing the spermatogenic cells. Thus, the Sertoli cells play a vital role in regulating the spermatogenic process. Our studies correlate retinoid action with the transactivation of genes which encode the transcription factors, Jun and Myb, in the Sertoli cells of the rat testis, a retinol-dependent organ. We examined the mRNA levels for the protooncogene, c-jun, a member of the AP-I transcription complex, as well as mRNA levels for the protooncogene, c-myb, following retinoid stimulation. The major changes observed were a significant up-regulation in c-jun mRNA beginning at 30 min which reached a four-fold peak over controls at 1 h while the c-myb mRNA level exhibited a delay in up-regulation which rose abruptly to a significant three-fold peak over controls at 1 h. Interestingly, a variation in transcript size for c-jun (5.4 kb) was also detected in rat Sertoli cells. The significant 50% rise in the c-jun mRNA levels at 30 min prior to the rapid rise in the c-myb message at 1 h suggests that Jun may be involved in the transactivation of c-myb gene expression. These data support the model that retinoid modulation of these immediate early genes is the first step in a process which initiates a cascade of vitamin A-inducible gene expression in rat Sertoli cells necessary for maintaining spermatogenesis.

Heterogeneity in induced thermal resistance of rat tumor cell clones.

Four 13762NF rat mammary adenocarcinoma clones were examined for their survival response to heating under conditions that induced transient thermal resistance (thermotolerance). Clones MTC and MTF7 were isolated from the subcutaneous locally growing tumor, whereas clones MTLn2 and MTLn3 were derived from spontaneous lung metastases. There was heterogeneity among these clones in thermotolerance induced by either fractionated 45 degrees C or continuous 42 degrees C heating, but the order of sensitivity was not necessarily the same. The clones developed thermal resistance at different rates and to different degrees within the same time intervals. There was heterogeneity between clones isolated from within either the primary site or metastatic lesions. However, clones derived from metastatic foci did not intrinsically acquire more or less thermotolerance to fractionated 45 degrees C or continuous 42 degrees C heating than did clones from the primary tumor. Further, there was no apparent relationship between any phenotypic properties that conferred more or less thermotolerance in vitro and any phenotypic properties that conferred enhanced metastatic success of these same clones by spontaneous (subcutaneous) or experimental (intravenous) routes in vivo. These tumor clones also differ in their karyotype, metastatic potential, cell surface features, sensitivity to x-irradiation and drugs, and ability to repair sublethal radiation damage. These results provide further credence to the concept that inherent heterogeneity within tumors may be as important in therapeutic success as other known modifiers of outcome such as site and treatment heterogeneity.

Heat-stress proteins and thermal resistance in rat mammary tumor cells.

Exposure of clone MTC rat 13672NF mammary adenocarcinoma cells to continuous heating at 42 degrees C or to heating for 20 min at 45 degrees C followed by incubation at 37 degrees C induced or enhanced synthesis of several heat-stress proteins (hsp) detectable by [3H]leucine pulse labeling, gel electrophoresis, and fluorography. Hsp synthesis occurred during development and expression of thermal resistance. For example, continuous heating of MTC cells at 42 degrees C after a rapid temperature transient (about 4 min) produced thermal resistance within 4 to 5 hr of initiation of heating. Hsp synthesis was observed within 2 hr of the cells reaching 42 degrees C and continued throughout 8 hr of heating; four major hsp appeared at nominal molecular weights of 112, 90, 70, and 22 kDa. A slow temperature transient from 37 degrees to 42 degrees C over a 3-hr period increased thermal resistance by a factor of about 2 relative to a rapid transient or "shock" to 42 degrees C. However, hsp synthesis was not significant during the slow heat transient and was either reduced (at 70 and 22 kDa) or not increased (at 112 and 90 kDa) compared with the rates of hsp synthesis at the same time intervals after the rapid transient to 42 degrees C. In these mammary tumor cells, no differences in the number of hsp were detected during heating at 42 degrees or after 45 degrees C heating. Other proteins did not appear to change their relative rates of synthesis, with the exception of a clear decrease in proteins with nominal molecular weights of histones H2A, H2B, H3, and H4. Hsp synthesis was not triggered by cold shock to 23 degrees or 0 degree C, or by radiation of from 2.5 to 10 Gy. Thus hypothermic stress did not enhance hsp synthesis nor were hsp nonspecifically associated with eventual cell lethality. In these experiments, the synthesis of hsp was generally correlated with the development of thermal resistance. Determining the quantity, function, and location of stress proteins may identify targets for thermal killing and resistance. However, one paradoxical observation remains to be resolved. Under the slow temperature transient conditions, the tumor cells attained more thermal resistance with generally reduced rates of hsp synthesis. These results have two possible implications: (a) one or more hsp were not directly related to thermal resistance, or (b) hsp were involved in thermal resistance but their relative rate of synthesis depended on the severity of the heat transient. The latter would imply that the cells made other regulatory or metabolic adjustments and either utilized the hsp more effectively or required less additional hsp.