[Alteration of isozyme gene expression during cell differentiation and oncogenesis]

Rat pyruvate kinase (PK) has four isozymes, called the M1-, M2-, L-, and R-types. The M1- and M2-type isozymes of PK are produced from the PKM gene by alternative splicing, whereas the L- and R-type isozymes of PK are produced from the PKL gene by use of different tissue-specific promoters. In early development, only M2-type PK expresses in all tissues. After late morphogenesis, M1-, L-, and R-type PK express tissue-specifically. In contrast, cell proliferation such as regenerating liver and oncogenesis lead to decrease or cessation of the expression of tissue-specific PK isozymes and to stimulation of the expression of M2-type PK. These phenomena from the point of view transcriptional regulatory apparatus of the PKM and PKL gene are discussed.