Abstract
The Prolactin-inducible-protein (PIP)/Gross Cystic Disease Fluid Protein-15 (GCDFP-15) gene is highly expressed in salivary, lacrimal and sweat glands and the protein abundantly found in the secretions that originate from these glands; saliva, tears and sweat. PIP is thus considered to be strategically located at sites viewed as the first port of entry for invading organisms. PIP is also found over-expressed under abnormal and pathological conditions of the breast and prostate. The function of PIP has yet to be defined but it has been implicated to play a role in immunity, with respect to bacterial and viral infection, cancer and fertility. Despite such predictive functions, there is still no clear demonstration of an immunoregulatory role for PIP. In this review we will focus on accumulating evidence that suggests a role for PIP in both innate and adaptive immunity. Moreover, we will discuss recent evidence that defines a modulatory role for PIP with regards to a CD4+ T cell immune response, identifying for the first time, a critical role for PIP in effective cell-mediated immunity against an intracellular pathogen.
Highlights
The human Prolactin-inducible-protein (PIP)/Gross Cystic Disease Fluid Protein-15 (GCDFP-15) was first reported by Haagensen et al [1] as an acidic protein found in abundance in gross cystic disease fluid of the breast
It was identified by Shiu and Iwasiow [2] as a glycoprotein secreted by human breast cancer cells in response to the lactogenic hormone prolactin [3,4] and was designated Prolactin-inducibleprotein (PIP)
PIP has been subsequently identified to be analogous to Glycoprotein-17 [5], Secretory Actin-Binding Protein (SABP) [6], and Extraparotid Glycoprotein (EP-GP) [7]
Summary
The human Prolactin-inducible-protein (PIP)/Gross Cystic Disease Fluid Protein-15 (GCDFP-15) was first. Reported by Haagensen et al [1] as an acidic protein found in abundance in gross cystic disease fluid of the breast. It was identified by Shiu and Iwasiow [2] as a glycoprotein secreted by human breast cancer cells in response to the lactogenic hormone prolactin [3,4] and was designated Prolactin-inducibleprotein (PIP). PIP is synthesized as a precursor polypeptide of 12.5 kDa and subsequent to the removal of the signal peptide; its size is reduced to 11 kDa [9]. The 14 kDa and the 16 kDa proteins are glycosylated forms of the 11 kDa protein
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