Sulfonation is an important reaction in the metabolism of numerous xenobiotics, drugs, and endogenous compounds. A supergene family of enzymes called sulfotransferases (SULTs) catalyze this reaction. In most cases, the addition of a sulfonate moiety to a compound increases its water solubility and decreases its biological activity. However, many of these enzymes are also capable of bioactivating procarcinogens to reactive electrophiles. In humans three SULT families, SULT1, SULT2, and SULT4, have been identified that contain at least thirteen distinct members. SULTs have a wide tissue distribution and act as a major detoxification enzyme system in adult and the developing human fetus. Nine crystal structures of human cytosolic SULTs have now been determined, and together with site-directed mutagenesis experiments and molecular modeling, we are now beginning to understand the factors that govern distinct but overlapping substrate specificities. These studies have also provided insight into the enzyme kinetics and inhibition characteristics of these enzymes. The regulation of human SULTs remains as one of the least explored areas of research in the field, though there have been some recent advances on the molecular transcription mechanism controlling the individual SULT promoters. Interindividual variation in sulfonation capacity may be important in determining an individual's response to xenobiotics, and recent studies have begun to suggest roles for SULT polymorphism in disease susceptibility. This review aims to provide a summary of our present understanding of the function of human cytosolic sulfotransferases.

The TGF-β signaling pathway has a complex role in regulating mammary carcinogenesis. Here we demonstrate that the type III TGF-β receptor (TβRIII, or betaglycan), a ubiquitously expressed TGF-β coreceptor, regulated breast cancer progression and metastasis. Most human breast cancers lost TβRIII expression, with loss of heterozygosity of the TGFBR3 gene locus correlating with decreased TβRIII expression. TβRIII expression decreased during breast cancer progression, and low TβRIII levels predicted decreased recurrence-free survival in breast cancer patients. Restoring TβRIII expression in breast cancer cells dramatically inhibited tumor invasiveness in vitro and tumor invasion, angiogenesis, and metastasis in vivo. TβRIII appeared to inhibit tumor invasion by undergoing ectodomain shedding and producing soluble TβRIII, which binds and sequesters TGF-β to decrease TGF-β signaling and reduce breast cancer cell invasion and tumor-induced angiogenesis. Our results indicate that loss of TβRIII through allelic imbalance is a frequent genetic event during human breast cancer development that increases metastatic potential.

Mammalian cells possess a multifaceted antioxidant enzyme system, which includes superoxide dismutases, catalase, the peroxiredoxin/thioredoxin and the glutathione peroxidase systems. The dichotomous role of reactive oxygen species and antioxidant enzymes in tumorigenesis and cancer progression complicates the use of small molecule antioxidants, pro-oxidants, and targeting of antioxidant enzymes as therapeutic approaches for cancer treatment. It also highlights the need for additional studies to investigate the role and regulation of these antioxidant enzymes in cancer. The focus of this review is on glutathione peroxidase 3 (GPx3), a selenoprotein, and the only extracellular GPx of a family of oxidoreductases that catalyze the detoxification of hydro- and soluble lipid hydroperoxides by reduced glutathione. In addition to summarizing the biochemical function, regulation, and disease associations of GPx3, we specifically discuss the role and regulation of systemic and tumor cell expressed GPx3 in cancer. From this it is evident that GPx3 has a dichotomous role in different tumor types, acting as both a tumor suppressor and pro-survival protein. Further studies are needed to examine how loss or gain of GPx3 specifically affects oxidant scavenging and redox signaling in the extracellular tumor microenvironment, and how GPx3 might be targeted for therapeutic intervention.

The transforming growth factor-β (TGF-β) signaling pathway has an important role in regulating normal prostate epithelium, inhibiting proliferation, differentiation, and both androgen deprivation–induced and androgen-independent apoptosis. During prostate cancer formation, most prostate cancer cells become resistant to these homeostatic effects of TGF-β. Although the loss of expression of either the type I (TβRI) or type II (TβRII) TGF-β receptor has been documented in ∼30% of prostate cancers, most prostate cancers become TGF-β resistant without mutation or deletion of TβRI, TβRII, or Smads2, 3, and 4, and thus, the mechanism of resistance remains to be defined. Here, we show that type III TGF-β receptor (TβRIII or betaglycan) expression is decreased or lost in the majority of human prostate cancers as compared with benign prostate tissue at both the mRNA and protein level. Loss of TβRIII expression correlates with advancing tumor stage and a higher probability of prostate-specific antigen (PSA) recurrence, suggesting a role in prostate cancer progression. The loss of TβRIII expression is mediated by the loss of heterozygosity at the TGFBR3 genomic locus and epigenetic regulation of the TβRIII promoter. Functionally, restoring TβRIII expression in prostate cancer cells potently decreases cell motility and cell invasion through Matrigel in vitro and prostate tumorigenicity in vivo. Taken together, these studies define the loss of TβRIII expression as a common event in human prostate cancer and suggest that this loss is important for prostate cancer progression through effects on cell motility, invasiveness, and tumorigenicity. [Cancer Res 2007;67(3):1090–8]

The essential role of ORAI1 channels in receptor-evoked Ca²⁺ signaling is well understood, yet little is known about the physiological activation of the ORAI channel trio natively expressed in all cells. The roles of ORAI2 and ORAI3 have remained obscure. We show that ORAI2 and ORAI3 channels play a critical role in mediating the regenerative Ca²⁺ oscillations induced by physiological receptor activation, yet ORAI1 is dispensable in generation of oscillations. We reveal that ORAI2 and ORAI3 channels multimerize with ORAI1 to expand the range of sensitivity of receptor-activated Ca²⁺ signals, reflecting their enhanced basal STIM1-binding and heightened Ca²⁺-dependent inactivation. This broadened bandwidth of Ca²⁺ influx is translated by cells into differential activation of NFAT1 and NFAT4 isoforms. Our results uncover a long-sought role for ORAI2 and ORAI3, revealing an intricate control mechanism whereby heteromerization of ORAI channels mediates graded Ca²⁺ signals that extend the agonist-sensitivity to fine-tune transcriptional control.