Steroidhormone receptor mechanism

The specific glucocorticoid receptor in the cytoplasm exists as a heterocomplex that contains the receptor in association with two subunits of the heat shock protein hsp 90, one subunit of the heat shock protein hsp 56, one subunit of the heat shock protein hsp 70 and an acidic 23 kDa protein.

The hormone binds to the hormone-binding domain that has been kept in an inactive state by the various heat shock proteins. Activation of the hormone-receptor complex by conformational change follows dissociation of heat shock proteins. Dimerisation of the hormone-receptor complexes relieves them from protection by the heat shock protein. The hormone-activated receptor translocates to the nucleus. Binding of dimer occurs to special DNA sequences known as hormone-responsive elements by the zinc finger area of the DNA-binding domain.

Classification of protein kinases

Cyclic nucleotide-dependent kinases cAMP-dependent protein kinases, types I and II cGMP-dependent protein kinases

Calcium-dependent kinases

Calcium/calmodulin-dependent protein kinases, types I, II, III Calcium/phospholipid-dependent protein kinases (protein kinase C): 9 isozymes

Cyclic nucleotide- and calcium-independent kinases

Casein kinases

Pyruvate dehydrogenase kinase Glycogen synthase kinase 3

Rhodopsin kinase: beta-adrenergic receptor kinase

Tyrosine-specific kinases

Growth factor receptors Non-receptor tyrosine kinases

5 Stimulation of transcription is mediated by transcription activation functions cr and influenced by the protein content of the cell, and by phosphorylation e (messenger ribonucleic acid (mRNA) synthesis and transport to ribosomes).

y The transcription rate of a specific protein's mRNA can be induced (up-

0 regulated) or suppressed (down-regulated). Stated otherwise, the expression of y genes can be either inhibited or enhanced by the hormone-receptor complex.

Cytoplasmic protein synthesis results in a specific cellular activity.

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