Spermatozoa are highly polarized cells with specific metabolic pathways compartmentalized in different regions. Previously, we hypothesized that glycolysis is organized in the fibrous sheath of the flagellum to provide ATP to dynein ATPases that generate motility and to protein kinases that regulate motility. Although a recent report suggested that glucose is not essential for murine sperm capacitation, we demonstrated that glucose (but not lactate or pyruvate) was necessary and sufficient to support the protein tyrosine phosphorylation events associated with capacitation. The effect of glucose on this signaling pathway was downstream of cAMP, and appeared to arise indirectly as a consequence of metabolism as opposed to a direct signaling effect. Moreover, the phosphorylation events were not affected by uncouplers of oxidative respiration, inhibitors of electron transfer, or by a lack of substrates for oxidative respiration in the medium. Further experiments aimed at identifying potential regulators of sperm glycolysis focused on a germ cell-specific isoform of hexokinase, HK1-SC, which localizes to the fibrous sheath. HK1-SC activity and biochemical localization did not change during sperm capacitation, suggesting that glycolysis in sperm is regulated either at the level of substrate availability or by downstream enzymes. These data support the hypothesis that ATP specifically produced by a compartmentalized glycolytic pathway in the principal piece of the flagellum, as opposed to ATP generated by mitochondria in the mid-piece, is strictly required for protein tyrosine phosphorylation events that take place during sperm capacitation. The relationship between these pathways suggests that spermatozoa offer a model system for the study of integration of compartmentalized metabolic and signaling pathways.Mammalian spermatozoa are highly differentiated cells that display extreme polarization of cellular architecture and function. For example, the sperm head has evolved to interact with the egg's extracellular matrix and plasma membrane, and contains the paternal genetic material, whereas the sperm flagellum acts to provide motility for these cells. In regard to this polarization of function, sperm have two major constraints. First, they have little cytoplasm, and therefore have a reduced ability to translocate metabolic intermediates or substrates from one region to another. In addition, they are transcriptionally inactive, and therefore cannot make new proteins in response to changing needs. To overcome these constraints, we, along with others, have hypothesized that sperm possess compartmentalized metabolic and signaling pathways in specific regions of the cell poised to function in a localized fashion (1-4).The most obvious example of metabolic compartmentalization in spermatozoa is that of oxidative respiration. This pathway is restricted to the mid-piece of the flagellum, because mitochondria are located solely in this region. Oxidative respiration provides the most efficient generation of ATP, yet the major si...

Cancer cells have defects in regulatory mechanisms that usually control cell proliferation and homeostasis. Different cancer cells share crucial alterations in cell physiology, which lead to malignant growth. Tumorigenesis or tumor growth requires a series of events that include constant cell proliferation, promotion of metastasis and invasion, stimulation of angiogenesis, evasion of tumor suppressor factors, as well as avoidance of cell death pathways. All these events in tumor progression may be regulated by growth factors produced by normal or malignant cells. The growth factor progranulin has significant biological effects in different types of cancer. This protein is a regulator of tumorigenesis because it stimulates cell proliferation, migration, invasion, angiogenesis, malignant transformation, resistance to anticancer drugs, and immune evasion. This review focuses on the biological effects of progranulin in several cancer models and provides evidence that this growth factor should be considered as a potential biomarker and target in cancer treatment.

Preimplantation mammalian embryos in culture secrete autocrine growth factors into the surrounding medium that, in turn, stimulate the development of the embryos. The full complement of these factors is unknown. Since one hallmark of embryo development is the formation of an epithelium, the trophectoderm, we tested the hypothesis that one such embryo-derived growth factor is acrogranin (epithelin/granulin precursor), a factor that possesses growth-regulatory activities principally toward epithelial cells. We found that acrogranin mRNA was expressed in preimplantation mouse embryos with the transcript levels rising to their highest point in blastocysts, coincident with the appearance of the trophectoderm. Indirect immunofluorescence confocal microscopy of preimplantation mouse embryos at different developmental stages revealed that acrogranin immunostaining was most concentrated in the trophectoderm of blastocysts. Immunoblotting and immunoprecipitation experiments demonstrated that the embryos secreted acrogranin into the surrounding medium. To determine how altering the levels of acrogranin in the culture medium surrounding the embryos might affect embryonic growth and development, acrogranin protein levels in the culture medium were decreased with a function-blocking antibody or increased by adding the purified acrogranin to the medium. In both a concentration-dependent and a reversible manner, affinity-purified anti-acrogranin antibody significantly inhibited the development of eight-cell embryos to the blastocyst stage compared to controls (no added immunoglobulin or nonspecific IgG). Furthermore, embryo cell numbers were significantly decreased in the presence of the highest concentrations of acrogranin antibody compared to control embryos. Exogenous acrogranin added to cultures of eight-cell embryos accelerated the time for the onset of cavitation, as well as stimulating the rate of blastocoel expansion and increasing the number of trophectoderm cells compared to controls. These results indicate that acrogranin can regulate the appearance of the epithelium in the developing mouse blastocyst, the growth of the trophectoderm, and/or the function of the embryonic epithelium.

Using cDNA microarray methodology, we have shown previously that transcripts of progranulin gene (Grn, also known as acrogranin), a recently identified autocrine growth factor, were upregulated in mouse blastocysts adhered to the filter membrane in an in vitro-culture system. In the present study, we investigated the expression and effects of progranulin on blastocyst hatching, adhesion, and embryo outgrowth during the peri-implantation period in the mouse. During this period, substantial amounts of Grn mRNA were present in both inner cell mass (ICM) and trophectoderm. Progranulin was localized exclusively to the surface of the trophectoderm in early and pre- and postadhesion blastocysts as well as in trophoblast cells and ICM of outgrowth embryos, being secreted as a single, 88-kDa form into the surrounding medium. NIH3T3 cells that had been transfected with a progranulin expression construct secreted the 88-kDa form of the protein, from which a 68-kDa form could be generated by deglycosylation. In vitro treatment of blastocysts with recombinant progranulin promoted blastocyst hatching, adhesion, and outgrowth, whereas rabbit anti-mouse progranulin immunoglobulin G reduced the incidence of blastocyst hatching, adhesion, and outgrowth. Studies of bromodeoxyuridine incorporation and immunodissection of the ICM revealed that progranulin was effective on the trophectoderm but not on the ICM. These results indicate that progranulin is an important factor for the processes of blastocyst hatching, adhesion, and outgrowth, and they suggest that the effects of progranulin on blastocyst adhesion and outgrowth may have been triggered by the previous action of progranulin to induce hatching of the blastocysts.