Proteinase inhibitor identification in the uteroglobin fraction of rabbit uterine secretion

Clara cell proteins

Clara cells are nonciliated, nonmucous, secretory cells of the pulmonary airways. These cells are known to secrete a variety of proteins, including Clara cell 10-kDa protein/uteroglobin. This protein consists of a homodimer of 70-77 amino acid polypeptides arranged in antiparallel fashion. In vitro testing suggests that the protein suppresses inflammation. The physiologic role of the protein remains to be determined.

Clara cell 10 kDa protein (CC10): comparison of structure and function to uteroglobin

The cellular localization, functional activities and structures of rat and human Clara cell 10 kDa proteins (CC10) are compared to rabbit uteroglobin. CC10 is present exclusively in the non-ciliated cells of the surface epithelium of the pulmonary airways, whereas uteroglobin is reported to be present in the lung and reproductive organs. There is about 55% identity between the amino acid sequences of rat CC10 and either rabbit uteroglobin or human CC10. The latter two have 61% identity. Using the known structure of uteroglobin as the model, correlations between the structure and function for this group of proteins are made. Substitution of the residues for the rat and human CC10 into the structure of uteroglobin suggests that these proteins may be members of a structurally homologous family. Some of the functional differences may be due to distortion of the hydrophobic pocket in the dimeric protein and a surface hypervariability located on one contiguous helix and beta turn. Rat CC10 and rabbit uteroglobin both, nearly equally, inhibit papain and bind progesterone. Human CC10 does not inhibit papain and has markedly lower progesterone binding (4.6% of rabbit uteroglobin). Antiinflammatory activity of synthetic peptides corresponding to a homologous sequence region of uteroglobin and the two Clara cell proteins was tested. The region chosen has sequence similarity to lipocortin I. The peptides not only failed to inhibit carrageenan-induced foot pad swelling but exacerbated it. All three proteins inhibit pancreatic phospholipase A2. The phospholipase A2 inhibitory effect of CC10 may be important in regulating the inflammatory responses in the lung.

The presence of the fifth component of complement (C5) in rabbit uterine flushings in relation to reproductive state

The fifth component of complement (C5) has been detected in rabbit uterine flushings. The C5 activity was evaluated using a hemolytic assay which requires the use of a C5-depleted reagent (C5D) prepared by affinity chromatography of normal human serum. In the absence of C5D, there was no hemolysis of antibody-sensitized erythrocytes by rabbit uterine flushings, whereas the presence of the C5D reagent resulted in substantial hemolysis. The amount of hemolysis was correlated with the reproductive state of the rabbits, with higher amounts of hemolysis (expressed per mg uterine flushing protein) evident in estrous rabbits. In addition, the amounts of immunoglobulin G (IgG), albumin, and total protein were also determined in the uterine flushings. The amounts of total protein and IgG were increased in day-6 pregnant animals compared to estrus while the amount of albumin per ml uterine flushing was not significantly changed.

Immunocytochemical localization of uteroglobin in the rabbit endometrium

Uteroglobin, the progesterone dependent pregnancy-characteristic endometrial protein in the rabbit, is found within the endometrial epithelium on the fourth and sixth day of pregnancy at the electron-microscopic level by use of the immunoperoxidase technique and a specific anti-uteroglobin serum from the sheep. As known from earlier studies, uteroglobin is the predominant protein synthesized of the endometrial secretion. In the present study, it is localized exclusively in the non-ciliated epithelial cells. A common route of secretory proteins within these cells is observed by uteroglobin labelling: rough endoplasmatic reticulum----Golgi complex----condensing vesicles----secretory products. Uteroglobin occurs in small vesicles on the trans-face of the Golgi complex, and in addition beneath the apical plasma membrane where it appears in membrane-bound vesicles, which apparently are extruded into the uterine lumen. Most of the uteroglobin is located in the luminal secretion. The distribution of intracellular uteroglobin is found only in cells of the basal endometrial gland, adjacent to the myometrium. The cytoplasm of uterine epithelial cells facing the cavum does not show uteroglobin reaction products.

Ultrastructural localization of uteroglobin immunoreactivity in rabbit lung and endometrium, and rat ventral prostate

Recent biochemical studies have demonstrated amino acid sequence homologies between uteroglobin from rabbit endometrium and prostatic binding protein from rat ventral prostate. We have studied the ultrastructural distribution of uteroglobin-immunoreactive material in rabbit lung and endometrium and rat ventral prostate using an uteroglobin antibody raised in guinea pigs. Secretory granules of bronchiolar Clara cells, endometrial non-ciliated cells and rat prostate secretory cells gave a positive immunoreaction when this antibody was used. The results indicate a close relationship of immunoreactive epitopes of proteins present in those secretory cells. The functional properties of these proteins (glycoproteins, steroid binding, androgen-dependent secretion) suggest a close functional relationship, for instance a surface action such as coating, capping, masking or lubrication.