Cathepsin d

 

To summarize use of glucan in tumoChahahahahar therapy:

summary of the role:

  • Procathepsin D and its activation peptide act as an autocrine mitogen in human lung and breast cancer-derived cell lines
  • The growth factor activity of procathepsin D can be localized in position 36-44 of the activation peptide
  • In vivo experiments demonstrated that anti-procathepsin D (or anti-36-44 AA fragment) antibodies can suppress the growth of lung and breast cancer in mice
  • Secretion of procathepsin D from the cancer cells correlates with level of invasiveness in vitro
  • The mitogenic activity of procathepsin D is not dependent on proteolytic activity or glycosylation
  • Both ribozymes and siRNA blocking pCD secretion also inhibits lung and breast cancer
  • Transfection of control cells with pCD cDNA will switch their mutagenicity
  • Various cytokines are involved in pCD-stimulated proliferation
  • Numerous genes (including NFkB2 and Cdc25) are involved in effects of pCD
  • The activation peptide of procathepsin D is a new potential target for inhibition of cancer growth
  • Release of activation peptide and subsequent formation of specific antibodies can be used for a simple cancer screening
Breast cancer is the leading cause of death in U.S. women age 40-55 . In the United States, more than 10% of women will develop breast cancer during their lifetime and this rate has increased dramatically in recent years. Several factors have been investigated for prognosis in previously diagnosed breast cancer, and some of them, such as receptors for estrogen and progesterone, are in clinical use. Independent prognostic factors also include cathepsin D.The synthesis of cathepsin D is controlled by steroid hormones. In breast cancer cell lines, cathepsin D expression is regulated by estrogens that interact at the promoter level. Unlike other members of the aspartic proteinase family, which are mostly secretory proteins, procathepsin D (pCD) is sorted to the lysosomes. Under normal physiologic conditions, neither procathepsin D nor cathepsin D are secreted, and each are found only intracellularly.


Cathepsin D (E.C.3.4.23.5.) is a soluble lysosomal aspartic proteinase. It is synthesized in the endoplasmic reticulum as a preprocathepsin D. Having a mannose-6-phosphate tag, procathepsin D is recognized by a mannose-6-phosphate receptor. Upon entering into an acidic lysosome, the single-chain procathepsin D (52 KDa) is activated to cathepsin D and subsequently to a mature two-chain cathepsin D (31 and 14 KDa, respectively). The two mannose-6-phosphate receptors involved in the lysosomal targeting of procathepsin D are expressed both intracellularly and on the outer cell membrane. The glycosylation is believed to be crucial for normal intracellular trafficking. The fundamental role of cathepsin D is to degrade intracellular and internalized proteins. Cathepsin D has been suggested to take part in antigen processing and in enzymatic generation of peptide hormones. The tissue-specific function of cathepsin D seems to be connected to the processing of prolactin. Rat mammary glands use this enzyme for the formation of biologically active fragments of prolactin. Cathepsin D is functional in a wide variety of tissues during their remodeling or regression, and in apoptosis.


The synthesis of cathepsin D is controlled by steroid hormones. Progesterone and its derivatives increase the rate of uterine cathepsin D synthesis, and in breast cancer cell lines, cathepsin D expression is regulated by estrogens that interact at the promoter level. In ER+ cell lines, procathepsin D is secreted only after estrogen stimulation. On the other hand, it is secreted constitutively in ER- cell lines. Unlike other members of the aspartic proteinase family, which are mostly secretory proteins, procathepsin D is sorted to the lysosomes. Under normal physiologic conditions, neither procathepsin D nor cathepsin D are secreted, and each are found only intracellularly.


Increased levels of cathepsin D (both at the mRNA and protein levels)  were first reported in several human neoplastic tissues in the mid-eighties. These findings generated intense research in a possible role for cathepsin D in neoplastic processes. A strong predictive value was found for cathepsin D concentrations in breast cancer as well as many other tumor types. However, despite numerous studies suggesting involvement of cathepsin D, the direct enzymatic involvement of mature cathepsin D in the invasiveness of breast cancer cells has never been demonstrated. The basis for the diagnostic or prognostic value of cathepsin D concentrations is controversial. At any given time, three different components of cathepsin D are present in breast tumor tissue: a) procathepsin D; b) mature enzyme cathepsin D; and c) the APpCD  protein that derives from procathepsin D during generation of cathepsin D. Furthermore, the monoclonal antibodies that have been used for visualization of cathepsin D in tissue samples react with both cathepsin D and procathepsin D. Western blotting distinguishes procathepsin D by molecular weight, revealing that most cathepsin D is in the form of procathepsin D. In addition, it has never been demonstrated that the secreted procathepsin D is converted to the mature enzyme in an extracellular milieu, which is not sufficiently acidic. It has been recommended that levels of cathepsin D be monitored as a prognostic indicator in breast cancer and used independent of classical prognostic parameters such as tumor size, histologic grade, lymph node status and steroid receptor expression. The significance of procathepsin D and cathepsin D levels in various other tumors such as endometrial adenocarcinoma, colon carcinoma, laryngeal tumors, carcinoma of thyroid tissue, prostate tumors and ovarian cancer has also been demonstrated, suggesting that this system might be involved in the metastatic growth of several other cancer cell types.


Procathepsin D is a major secreted glycoprotein in some human breast cancer cell lines such as MCF-7 and ZR-75-1. Vignon et al. first proposed that procathepsin D served as a growth factor for these cancer cell lines. Moreover,  several clinical studies suggested a potential role for this molecule in metastasis, because its concentration in primary tumors correlated with an increased incidence of tumor metastases.  In nude mice, it was shown that rat tumor cells were converted from low to high metastatic potential by transfection with the cDNA for human cathepsin D indicating the role of procathepsin D in metastases.


Our own work on the role of procathepsin D in breast cancer began in 1991. We found that this enzymatically inactive zymogen acts as an autocrine growth factor specific for breast cancer-derived cells. Furthermore, the growth of breast cancer cells in vivo could be inhibited by anti-procathepsin D antibodies. This function was mediated through a specific receptor expressed on all eight human breast cancer cell lines examined. This receptor was found to be distinct from the well known mannose-6-phosphate receptor, which has been shown to function as the cathepsin D receptor in most other systems. The parts of the procathepsin D molecule responsible for its mitogenic activity were localized near to amino acids 27-44 of the activation peptide (APpCD) sequence. In all our experiments, the mature enzyme cathepsin D had no role in metastasis. Accordingly, the current proposal is focused entirely on the biological activity of procathepsin D and no experiments involving cathepsin D or its enzymatic activity are involved.


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