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Processing and Estrogen Regulation of the 52-Kilodalton Protein inside MCF₇ Breast Cancer Cells^*

Institut National de la Sante et de la Recherche Medicate, Unite d’Endocrinologie Cellulaire et Moteculaire 34100 Montpellier, France

Address all correspondence and requests for reprints to: Dr. Henri Rochefort, INSERM, Unite d’Endocrinologie Cellulaire et Moleculaire, U-148, 60 rue de Navacelles, 34100 Montpellier, France.

Abstract

A 52K glycoprotein is secreted by human breast cancer cells in culture after estrogen stimulation. Using monoclonal antibodies, we have quantitated and characterized the corresponding proteins of the cell compartment. Using pulsechase experiments, we have shown that about 40% of the 52K protein is secreted, the majority being successively processed into a 48K and a 34K protein. This last protein is very stable. The processing is inhibited by lysosomotropic agents and leupeptin, suggesting that it occurs in acidic vesicles, such as lysosomes or endosomes.

Estradiol increased the intracellular level of immunoreactive 52K related proteins by 4-fold. Its effect is, however, more obvious in the medium, since there is a constitutive level in the cell. The stimulatory effects of estradiol on [³H]mannose and [³⁵S]methionine incorporation into these proteins were similar and the endoglycosydase H sensitivity of the proteins was not altered, suggesting that estradiol did not modulate the glycosylation step. Antiestrogens did not stimulate synthesis and glycosylation of the 52K related proteins. Estradiol also increased the stability of the 52K precursor as well as that of total proteins.

We conclude that the secreted 52K protein is the precursor of two cellular proteins of 48K and 34K. Estradiol stimulates both the intracellular accumulation of these proteins and the secretion of the precursor. (Endocrinology 119: 2773–2782, 1986)

Footnotes

^* Preliminary results have been reported at the 67th Annual Meeting of The Endocrine Society, Baltimore, MD, 1985 (Abstract 754), in "Breast Cancer: Origins, Detection and Treatment" [Proceedings of the Biennial International Breast Cancer Research Conference, Rich, M.A., et al. (eds), Martinus Nijhoff, Boston, pp. 57–68, 1986], and in "Hormone and Cell Regulation" (10th European Symposium on Hormones and Cell Regulation; Libbey, London, 1986). This work was supported by INSERM and the Ministere de la Recherche et de la Technologie (to M.M.).

Received March 21, 1986.

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