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Apocrine Secretion — Fact or Artifact?

1999; Elsevier BV; Volume: 181; Issue: 5 Linguagem: Inglês

10.1016/s0940-9602(99)80020-x

1618-0402

Gerhard Aumüller, Beate Wilhelm, Juergen Seitz,

Fibroblast Growth Factor Research

In this review, the history of apocrine secretion and the essential categories are briefly mentioned and fused into a more generally applicable terminology. Using the coagulating gland of the male rat as a model, the mechanisms of apocrine secretion, the participation of the cytoskeleton in the formation of the apocrine blebs ("aposomes") and the structure of the secretory proteins, as well as the hormonal regulation of their biosynthesis are described. Apocrine secreted proteins share the following peculiarities: (i) Their biosynthesis and post-trans lational modification (including an unusual form of glycosylation) take place in the cytoplasm. (ii) Intracellu lar transport proceeds without participation of the endo membrane system, the Golgi apparatus and secretion granules. (iii) Blood serum derived transsudated albumin entering the secretory cells functions as a carrier of the apocrine-released proteins. Some common molecular features are specific for the apocrine-synthesized proteins studied so far by our group: (a) Their primary sequence is synthesized without a signal peptide. (b) Their N-termi nus is blocked by acetylation. (c) The substituting gly canes are neither O- nor N-linked. (d) At least one of the apocrine-synthesized proteins (secretory transglutami nase) contains a glycerol-phosphoinositol (GPI-) anchor. There are a number of still open questions in apocrine secretion, pertaining to (I) the intracellular transport and targeting of the proteins, (II) the coordination of simultaneously occurring apocrine and merocrine secretion in several of the apocrine glands, (III) the biosynthesis of the apical membrane proteins surrounding the aposomes and (IV) the repair mechanisms of the apical cell pole following the release of the aposomes. In conclusion, apocrine release is not an artifact but rather an alternative extrusion mechanism of soluble and membrane-associated proteins, usually linked with sex- or reproductive related glands, such as the prostate, the mammary glands, apocrine sweat glands or epididymis.