The keratin pattern of newborn mouse epidermis was investigated during terminal differentiation. In highly pure fractions of basal and suprabasal cells, obtained by Percoll density gradient centrifugation, we identified two sets of mRNA-encoded proteins: a basal set of 58.5, 52, and 47 kd subunits and a suprabasal set of 67 and 60 kd subunits. The large subunits of each set were alkaline to neutral, while the small subunits were acidic. Polyclonal antibodies against the suprabasal, acidic 60 kd protein and the basal, alkaline 58.5 kd protein selectively recognized their antigens in immunoblots of NEPHGE -resolved keratins and decorated the corresponding epidermal compartments in frozen sections. The antibody to the suprabasal 60 kd protein also recognized distinct cells in the basal cell layer. Quantification of this cell population revealed a 10% cell fraction, morphologically indistinguishable from the total cell population, that, in addition to expressing basal keratin proteins, was already synthesizing suprabasal keratin subunits.

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Thromboplastic and fibrinolytic activities of 14 lines of cultured human cancer cells were estimated by modified Astrup's methods. High tissue thromboplastic activity was found in one line of urinary-bladder cancer, 2 lines of gastric cancer and one line of lung cancer, but no activity was found in 6 lines of lung cancer. High fibrinolytic activity was noted in one line of gastric cancer and 2 lines of lung cancer, but no activity was seen in 6 lines of lung cancer and one line of gastric cancer. No plasmin activity was found. The tumour cell lines could be classified into 3 groups on the basis of the 2 activities. Cancer cell lines could also be classified into 2 groups: with high or low release of thromboplastin into culture media. Fibrinolytic activity was found in the culture media of all cell lines with high fibrinolytic activity. Fibrinolytic activity, but not thromboplastic activity, seemed to be influenced by the constituents of culture media. No definite correlation was found between the 2 activities and the histological types of the parent tumours of the cultured cells. Images Fig. 1 Fig. 2 Fig. 3

These results indicate that thromboplastic activity of tumour cells might be important in forming microthrombi in the lodgement phase and might be one of the factors facilitating blood-borne metastasis.

The internal epithelium of mouse forestomach represents a fully keratinized tissue that has many morphological aspects in common with the integumental epidermis. In the present study we have, therefore, analyzed keratin expression in the total epithelium, in subfractions of basal cells and in living and dead suprabasal cells that were obtained by Percoll density gradient centrifugation of trypsin-dissociated forestomach keratinocytes. The keratin analysis revealed that basal forestomach keratinocytes synthesize the same keratin types as basal epidermal cells (60000, 52,000 and 47,000 daltons), whereas differentiating cells contain both the epidermal suprabasal keratin pair (67,000 and 59,000 daltons) and the suprabasal keratin pair characteristic for other internal squamous epithelia (57,000 and 47,000 daltons). Indirect immunofluorescence using an antibody recognizing the members of the epidermal-type suprabasal keratin pair and in-situ-hybridization experiments using specific cDNA probes for the members of the internal-type keratin pair showed that the two keratin pairs are uniformly coexpressed in living suprabasal forestomach keratinocytes. Furthermore, it could be shown that distinct cells in the basal cell layer acquire the ability to express both the 67,000/59,000 dalton and the 57,000/47,000 dalton keratin pair and that some basal cells apparently lose the ability to synthesize mRNAs for basal keratins.

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Summary.-Lewis lung carcinoma cells were implanted in the foot-pads of mice and the effects of the plasminogen-plasmin inhibitor tranexamic acid (t-AMCHA) and of the plasminogen activator urokinase on metastasis were examined by electron microscopy. The intravascular tumour cells were not associated with thrombus formation in either control or urokinase -treated mice. Polymerized fibrin deposition around tumour cells and thrombi composed of fibrin and platelets was observed only in the mice given t-AMCHA. This suggests that the inhibition of fibrinolysis by tACC caused fibrin deposition and thrombus formation around intravascular tumour cells, which prevented release of the cells from primary foci to form secondary tumours. On the other hand, fibrinolysis induced by urokinase prevented thrombus formation, and accelerated cell release from primary foci.

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