The Fer tyrosine kinase protects sperm from spontaneous acrosome reaction.

The physiological acrosome reaction occurs after mammalian spermatozoa undergo a process called capacitation in the female reproductive tract. Only acrosome reacted spermatozoon can penetrate the egg zona-pellucida and fertilize the egg. Sperm also contain several mechanisms that protect it from undergoing spontaneous acrosome reaction (sAR), a process that can occur in sperm before reaching proximity to the egg and that abrogates fertilization. We previously showed that calmodulin-kinase II (CaMKII) and phospholipase D (PLD) are involved in preventing sAR through two distinct pathways that enhance F-actin formation during capacitation. Here, we describe a novel additional pathway involving the tyrosine kinase Fer in a mechanism that also prevents sAR by enhancing actin polymerization during sperm capacitation. We further show that protein-kinase A (PKA) and the tyrosine-kinase Src, as well as PLD, direct Fer phosphorylation/activation. Activated Fer inhibits the Ser/Thr phosphatase PP1, thereby leading to CaMKII activation, actin polymerization, and sAR inhibition.

Fer and FerT: A New Regulatory Link between Sperm and Cancer Cells.

Fer and its sperm and cancer specific variant, FerT, are non-receptor tyrosine kinases which play roles in cancer progression and metastasis. Recent studies have shed light on the regulatory role of these kinases in ensuring proper sperm function. Comparison of the regulatory cascades in which Fer and FerT are engaged in sperm and cancer cells presents an interesting picture, in which similar regulatory interactions of these enzymes are integrated in a similar or different regulatory context in the two cell types. These diverse compositions extend from the involvement of Fer in modulation of actin cytoskeleton integrity and function, to the unique regulatory interactions of Fer with PARP-1 and the PP1 phosphatase. Furthermore, recent findings link the metabolic regulatory roles of Fer and FerT in sperm and cancer cells. In the current review, we discuss the above detailed aspects, which portray Fer and FerT as new regulatory links between sperm and malignant cells. This perspective view can endow us with new analytical and research tools that will deepen our understanding of the regulatory trajectories and networks that govern these two multi-layered systems.

TMF1 is upregulated by insulin and is required for a sustained glucose homeostasis.

Insulin-regulated glucose homeostasis is a critical and intricate physiological process, of which not all regulatory components have been deciphered. One of the key players in modulating glucose uptake by cells is the glucose transporter-GLUT4. In this study, we aimed to explore the regulatory role of the trans-Golgi-associated protein-TATA Element Modulatory Factor (TMF1) in the GLUT4 mediated, insulin-directed glucose uptake. By establishing and using TMF1-/- myoblasts and mice, we examined the effect of TMF1 absence on the insulin driven functioning of GLUT4. We show that TMF1 is upregulated by insulin in myoblasts, and is essential for the formation of insulin responsive, glucose transporter GLUT4-containing vesicles. Absence of TMF1 leads to the retention of GLUT4 in perinuclear compartments, and to severe impairment of insulin-stimulated GLUT4 trafficking throughout the cytoplasm and to the cell plasma membrane. Accordingly, glucose uptake is impaired in TMF1-/- cells, and TMF1-/- mice are hyperglycemic. This is reflected by the mice impaired blood glucose clearance and increased blood glucose level. Correspondingly, TMF1-/- animals are leaner than their normal littermates. Thus, TMF1 is a novel effector of insulin-regulated glucose homeostasis, and dys-functioning of this protein may contribute to the onset of a diabetes-like disorder.

Loss of Fer Jeopardizes Metabolic Plasticity and Mitochondrial Homeostasis in Lung and Breast Carcinoma Cells.

Metabolic plasticity is a hallmark of the ability of metastatic cancer cells to survive under stressful conditions. The intracellular Fer kinase is a selective constituent of the reprogramed mitochondria and metabolic system of cancer cells. In the current work, we deciphered the modulatory roles of Fer in the reprogrammed metabolic systems of metastatic, lung (H358), non-small cell lung cancer (NSCLC), and breast (MDA-MB-231), triple-negative breast cancer (TNBC), carcinoma cells. We show that H358 cells devoid of Fer (H358ΔFer), strictly depend on glucose for their proliferation and growth, and fail to compensate for glucose withdrawal by oxidizing and metabolizing glutamine. Furthermore, glucose deficiency caused increased reactive oxygen species (ROS) production and induction of a DNA damage response (DDR), accompanied by the onset of apoptosis and attenuated cell-cycle progression. Analysis of mitochondrial function revealed impaired respiratory and electron transport chain (ETC) complex 1 (comp. I) activity in the Fer-deficient H358ΔFer cells. This was manifested by decreased levels of NAD+ and ATP and relatively low abundance of tricarboxylic acid (TCA) cycle metabolites. Impaired electron transport chain comp. I activity and dependence on glucose were also confirmed in Fer-deficient, MDA-MB-231ΔFer cells. Although both H358ΔFer and MDA-MB-231ΔFer cells showed a decreased aspartate level, this seemed to be compensated by the predominance of pyrimidines synthesis over the urea cycle progression. Notably, absence of Fer significantly impeded the growth of H358ΔFer and MDA-MB-231ΔFer xenografts in mice provided with a carb-deficient, ketogenic diet. Thus, Fer plays a key role in the sustention of metabolic plasticity of malignant cells. In compliance with this notion, targeting Fer attenuates the progression of H358 and MDA-MB-231 tumors, an effect that is potentiated by a glucose-restrictive diet.

Reprogrammed and transmissible intestinal microbiota confer diminished susceptibility to induced colitis in TMF-/- mice.

Tata Element Modulatory Factor (TMF/ARA160) is a multifunctional Golgi-associated protein, which accumulates in colonic enterocytes and goblet cells. Mice lacking TMF/ARA160 (TMF(-/-)) produce thick and uniform colonic mucus that resists adherent bacterial colonization and diminishes susceptibility of these mice to induced acute colitis, through a mechanism that is not fully understood. Here, we show that mucus secretion by goblet cells is altered in the colon of TMF(-/-) mice, resulting in the formation of a highly oligomerized colonic gel-forming mucin, MUC2. Microbiome analysis revealed a shift in the microbiota of TMF(-/-) mice leading to predominance of the Firmicutes phylum and a significantly higher abundance of probiotic beneficial bacterial species. Notably, this trait was transmissible, and when cohoused with wild-type animals, TMF(-/-) mice influenced the microbiota and diminished the susceptibility of wild-type mice to chemically induced dextran sulfate sodium colitis. Thus, altered mucus secretion in TMF(-/-) mouse colons is accompanied by a reprogrammed intestinal microbiota, leading to a transmissible reduced sensitivity to induced colitis.

Intronic promoter drives the BORIS-regulated expression of FerT in colon carcinoma cells.

Fer is an intracellular tyrosine kinase that accumulates in most mammalian tissues. A truncated variant of Fer, FerT, is uniquely detected in spermatogenic cells and is absent from normal somatic tissues. Here, we show that in addition to Fer, FerT also accumulates in CC cells and in metastases derived from colorectal tumors, but not in normal human cells. Thus, FerT is a new member of the CTA protein family. Transcription of the ferT gene in CC cells was found to be driven by an intronic promoter residing in intron 10 of the fer gene and to be regulated by another CTA, the Brother of the Regulator of Imprinted Sites (BORIS) transcription factor. BORIS binds to the ferT promoter and down-regulation of BORIS significantly decreases the expression of ferT in CC cells. Accumulation of the ferT RNA was also regulated by the DNA methylation status and paralleled the expression profile of the boris transcript. Accordingly, the intronic ferT promoter was found to be hypomethylated in cancer cells expressing the FerT protein, by comparison with non-expressers. Collectively, we show here that FerT is a new CTA whose accumulation in CC cells, commonly considered low CTA expressers, is controlled by a novel transcription regulatory mechanism.

Loss of TMF/ARA160 protein renders colonic mucus refractory to bacterial colonization and diminishes intestinal susceptibility to acute colitis.

TMF/ARA160 is a Golgi-associated protein with several cellular functions, among them direction of the NF-κB subunit, p65 RelA, to ubiquitination and proteasomal degradation in stressed cells. We sought to investigate the role of TMF/ARA160 under imposed stress conditions in vivo. TMF(-/-) and wild-type (WT) mice were treated with the ulcerative agent dextran sulfate sodium (DSS), and the severity of the inflicted acute colitis was determined. TMF(-/-) mice were found to be significantly less susceptible to DSS-induced colitis, with profoundly less bacterial penetration into the colonic epithelia. Surprisingly, unlike in WT mice, no bacterial colonies were visualized in colons of healthy untreated TMF(-/-) mice, indicating the constitutive resistance of TMF(-/-) colonic mucus to bacterial retention and penetration. Gene expression analysis of colon tissues from unchallenged TMF(-/-) mice revealed 5-fold elevated transcription of the muc2 gene, which encodes the major component of the colonic mucus gel, the MUC2 mucin. Accordingly, the morphology of the colonic mucus in TMF(-/-) mice was found to differ from the mucus structure in WT colons. The NF-κB subunit, p65, a well known transcription inducer of muc2, was up-regulated significantly in TMF(-/-) intestinal epithelial cells. However, this did not cause spontaneous inflammation or increased colonic crypt cell proliferation. Collectively, our findings demonstrate that absence of TMF/ARA160 renders the colonic mucus refractory to bacterial colonization and the large intestine less susceptible to the onset of colitis.

A Novel Score-Based Approach by Using Routine Laboratory Tests for Accurate Diagnosis of Spontaneous Bacterial Peritonitis (SBP) in Cirrhotic Patients.

Background: Spontaneous Bacterial Peritonitis (SBP) poses a significant risk to cirrhosis patients with ascites, emphasizing the critical need for early detection and intervention. This retrospective observational study spanning a decade aimed to devise predictive models for SBP using routine laboratory tests. Additionally, it aimed to propose a novel scoring system to aid SBP diagnosis. Methods: Data analysis encompassed 229 adult cirrhotic patients hospitalized for ascites between 2012 and 2021. Exclusions eliminated cases of secondary ascites unrelated to liver cirrhosis. Patients were categorized into SBP-positive (n=110) and SBP-negative (n=119) groups. Comparative analysis of demographic details and various laboratory indicators (Neutrophil-to-Lymphocyte Ratio (NLR), Mean Platelet Volume (MPV), C-Reactive Protein (CRP), Platelet (PLT), Alanine Transaminase (ALT), Aspartate Amino Transferase (AST), Potassium (K), Sodium (Na), Total Bilirubin (TB) and International Normalized Ratio (INR) was performed between the groups. The study presented effective SBP prediction models for prompt diagnosis and treatment: a multivariate logistic regression model and a simple scoring system. Findings: The study advocates early diagnosis and rapid treatment for all cirrhotic patients with ascites, regardless of cirrhosis stage. Furthermore, it recommends initiating SBP treatment for patients scoring 2-3 in the proposed scoring system while excluding SBP findings for those scoring zero. Conclusion: Combining age, sex, and specific laboratory tests (MPV, NLR, CRP, TB, and INR) within random forest models and a simple scoring system enables swift and accurate SBP diagnosis.

TMF/ARA160: A key regulator of sperm development.

TMF/ARA160 is a Golgi-associated protein to which several cellular activities have been attributed. These include, trafficking of Golgi-derived vesicles and E3 ubiquitin ligase activity. Here we show that TMF/ARA160 is required for the onset of key processes which underlie the development of mature sperm in mammals. TMF/ARA160 is highly expressed in specific spermatogenic stages. While the protein is not detected in the spermatogenic progenitor cells - spermatogonia, it accumulates in the Golgi of spermatocytes and spermatids but then disappears and is absent from spermatozoa and epididymal sperm cells. Mice that are homozygous null for TMF develop normally are healthy and the females are fertile. However, the males are sterile and their spermatids suffer from several developmental defects. They lack homing of Golgi-derived proacrosomal vesicles to the perinuclear surface, resulting in spermatozoa and epididymal sperm cells which lack acrosome. In a later developmental stage, the cytoplasm is not properly removed, thus resulting in spermatids which bare the nucleus with tightly packed DNA, surrounded by a cytoplasm. Finally, the spermatozoa of TMF(-/-) mice also suffer from misshapen heads, tails coiling around the sperm heads, and lack of motility. Taken together our findings portray TMF/ARA160 as a key regulator which is essential for the onset of key events in the differentiation and maturation of mammalian sperm and whose absence severely compromises their ability to fertilize ova.

Deleterious mutations in the Zinc-Finger 469 gene cause brittle cornea syndrome.

Brittle cornea syndrome (BCS) is an autosomal-recessive disorder characterized by a thin cornea that tends to perforate, causing progressive visual loss and blindness. Additional systemic symptoms such as joint hypermotility, hyperlaxity of the skin, and kyphoscoliosis place BCS among the connective-tissue disorders. Previously, we assigned the disease gene to a 4.7 Mb interval on chromosome 16q24. In order to clone the BCS gene, we first narrowed the disease locus to a 2.8 Mb interval and systematically sequenced genes expressed in connective tissue in this chromosomal segment. We have identified two frameshift mutations in the Zinc-Finger 469 gene (ZNF469). In five unrelated patients of Tunisian Jewish ancestry, we found a 1 bp deletion at position 5943 (5943 delA), and in an inbred Palestinian family we detected a single-nucleotide deletion at position 9527 (9527 delG). The function of ZNF469 is unknown. However, a 30% homology to a number of collagens suggests that it could act as a transcription factor involved in the synthesis and/or organization of collagen fibers.

Fer and FerT Govern Mitochondrial Susceptibility to Metformin and Hypoxic Stress in Colon and Lung Carcinoma Cells.

Aerobic glycolysis is an important metabolic adaptation of cancer cells. However, there is growing evidence that reprogrammed mitochondria also play an important metabolic role in metastatic dissemination. Two constituents of the reprogrammed mitochondria of cancer cells are the intracellular tyrosine kinase Fer and its cancer- and sperm-specific variant, FerT. Here, we show that Fer and FerT control mitochondrial susceptibility to therapeutic and hypoxic stress in metastatic colon (SW620) and non-small cell lung cancer (NSCLC-H1299) cells. Fer- and FerT-deficient SW620 and H1299 cells (SW∆Fer/FerT and H∆Fer/FerT cells, respectively) become highly sensitive to metformin treatment and to hypoxia under glucose-restrictive conditions. Metformin impaired mitochondrial functioning that was accompanied by ATP deficiency and robust death in SW∆Fer/FerT and H∆Fer/FerT cells compared to the parental SW620 and H1299 cells. Notably, selective knockout of the fer gene without affecting FerT expression reduced sensitivity to metformin and hypoxia seen in SW∆Fer/FerT cells. Thus, Fer and FerT modulate the mitochondrial susceptibility of metastatic cancer cells to hypoxia and metformin. Targeting Fer/FerT may therefore provide a novel anticancer treatment by efficient, selective, and more versatile disruption of mitochondrial function in malignant cells.

Single nucleotide polymorphisms in miRNA binding sites and miRNA genes as breast/ovarian cancer risk modifiers in Jewish high-risk women.

We hypothesized that aberrant gene silencing by miRNA may affect mutant BRCA penetrance. To test this notion, frequency of single nucleotide polymorphisms (SNPs; n = 42) within predicted miRNA binding sites or miRNA precursors were determined and compared in 363 BRCA1 mutation carriers: asymptomatic (n = 160), breast cancer (n = 140) and ovarian cancer (n = 63) patients, and in 125 BRCA2 mutation carriers: asymptomatic (n = 48), breast cancer (n = 58) and ovarian cancer (n = 19) patients. Overall, 16 of 42 SNPs were polymorphic, 11 had a minor allele frequency greater than 5% and 9 of them maintained the Hardy-Weinberg Equilibrium. Based on Cox regression and Kaplan-Meier analyses, statistically significant differences were noted in BRCA2 mutation carriers by health status in 3 SNPs: CC homozygosity at rs6505162 increased ovarian cancer risk (RR 2.77; p = 0.028; 95% CI, 1.11-6.9); heterozygote SNP carriers of rs11169571 had an approximately 2 fold increased risk for developing breast/ovarian cancer, whereas heterozygotes of the rs895819 SNP had an approximately 50% reduced risk for developing breast/ovarian cancer. This study provides preliminary evidence for another regulatory level of penetrance of deleterious mutations in cancer predisposition genes.

TMF/ARA160 downregulates proangiogenic genes and attenuates the progression of PC3 xenografts.

TMF/ARA160 is a Golgi-associated protein whose level is downregulated in solid tumors. TMF changes its subcellular localization on exposure of cells to stress cues, thereby, directing proteins, such as the key transcription factor, Stat3, to proteasomal degradation. Here, we show that enforced ectopic expression of HA-TMF in PC3 prostate carcinoma cells, which do not express Stat3, significantly attenuated the development and growth of xenograft tumors elicited by these cells in athymic mice. Immunohistochemical analysis revealed impaired angiogenesis and accelerated onset of apoptosis in the HA-TMF-expressing tumors. RNA expression profiling revealed the downregulation of several proangiogenic genes in HA-TMF-expressing xenografts. Among these were the interleukin-8 and interleukin-1beta genes, whose expression is controlled by nuclear factor-kB. The level of the nuclear factor-kB component, p65/RelA, was decreased in HA-TMF-expressing xenografts, and TMF was found to direct the ubiquitination and proteasomal degradation of p65/RelA in metabolically stressed PC3 clones. Taken together, our findings indicate that TMF/ARA160 is a regulator of key transcription factors under metabolic constraints, thereby affecting angiogenesis and progression of solid tumors, which are subjected to metabolic stress.

Promoter methylation patterns of ATM, ATR, BRCA1, BRCA2 and p53 as putative cancer risk modifiers in Jewish BRCA1/BRCA2 mutation carriers.

BRCA1/BRCA2 germline mutations substantially increase breast and ovarian cancer risk, yet penetrance is incomplete. We hypothesized that germline epigenetic gene silencing may affect mutant BRCA1/2 penetrance. To test this notion, we determined the methylation status, using methylation-specific quantitative PCR of the promoter in putative modifier genes: BRCA1, BRCA2, ATM, ATR and P53 in Jewish BRCA1/BRCA2 mutation carriers with (n = 41) or without (n = 48) breast cancer, in sporadic breast cancer (n = 52), and healthy controls (n = 89). Promoter hypermethylation was detected only in the BRCA1 promotor in 5.6-7.3% in each of the four subsets of participants, regardless of health and BRCA1/2 status.Germline promoter hypermethylation in the BRCA1 gene can be detected in about 5% of the female Israeli Jewish population, regardless of the BRCA1/2 status. The significance of this observation is yet to be determined.

Novel involvement of the immunomodulator AS101 in IL-10 signaling, via the tyrosine kinase Fer.

Interleukin-10 (IL-10) plays a major proliferative role in many tumors, and activates the transcription factor Stat3 by tyrosine phosphorylation. The immunomodulator ammonium trichloro (dioxoethylene-o,o') tellurate (AS101) has a direct antitumor activity, and is able to sensitize several tumors to chemotherapy, by inhibiting the tumor IL-10 autocrine loop. The tyrosine kinase Fer is essential for the proliferation of numerous malignant cell lines and in some cases was related to Stat3 activation. This article examined the role of AS101 in IL-10 signaling, and the correlation between Fer and Stat3, in human peripheral blood mononuclear cells (PBMC). We show that Fer was associated with Stat3 in PBMC and RAW 264.7, a macrophage cell line. Recombinant IL-10 (rIL-10) increased the tyrosine phosphorylation of Stat3, upregulated the levels of Fer, and increased the association of Fer with phosphorylated Stat3 (pYStat3). All the activities of IL-10 mentioned above were reversed by AS101. The effects conferred by AS101 were totally abolished by exogenous addition of rIL-10. These results indicate that AS101 downregulates the Stat3 IL-10 loop, and inhibits Fer association with pYStat3. We conclude that anti-IL-10 treatment using AS101, may be beneficial in certain malignancies and other pathologies in which IL-10 secretion is elevated and Stat3 is continuously phosphorylated.

A novel Fer/FerT targeting compound selectively evokes metabolic stress and necrotic death in malignant cells.

Disruption of the reprogrammed energy management system of malignant cells is a prioritized goal of targeted cancer therapy. Two regulators of this system are the Fer kinase, and its cancer cell specific variant, FerT, both residing in subcellular compartments including the mitochondrial electron transport chain. Here, we show that a newly developed inhibitor of Fer and FerT, E260, selectively evokes metabolic stress in cancer cells by imposing mitochondrial dysfunction and deformation, and onset of energy-consuming autophagy which decreases the cellular ATP level. Notably, Fer was also found to associate with PARP-1 and E260 disrupted this association thereby leading to PARP-1 activation. The cooperative intervention with these metabolic pathways leads to energy crisis and necrotic death in malignant, but not in normal human cells, and to the suppression of tumors growth in vivo. Thus, E260 is a new anti-cancer agent which imposes metabolic stress and cellular death in cancer cells.The tyrosine-kinases Fer/FerT associate with the mitochondrial electron transport chain in cancer cells supporting their metabolic reprogramming. Here the authors discover a compound that disrupts Fer /FerT activity and selectively induces cell death of cancer cell lines displaying anti-tumor activity in vivo.

Mitochondrial OXPHOS Induced by RB1 Deficiency in Breast Cancer: Implications for Anabolic Metabolism, Stemness, and Metastasis.

A switch from catabolic to anabolic metabolism, a major hallmark of cancer, enables rapid cell duplication, and is driven by multiple oncogenic alterations, including PIK3CA mutation, MYC amplification, and TP53 loss. However, tumor growth requires active mitochondrial function and oxidative phosphorylation (OXPHOS). Recently, loss of the retinoblastoma (RB1) tumor suppressor in breast cancer was shown to induce mitochondrial protein translation (MPT) and OXPHOS. Here, we discuss how increased OXPHOS can enhance anabolic metabolism and cell proliferation, as well as cancer stemness and metastasis. Mitochondrial STAT3, FER/FER-T, and CHCHD2 are also implicated in OXPHOS. We propose that RB1 loss represents a prototypic oncogenic alteration that promotes OXPHOS, that aggressive tumors acquire lethal combinations of oncogenes and tumor suppressors that stimulate anabolism versus OXPHOS, and that targeting both metabolic pathways would be therapeutic.

trnp: A conserved mammalian gene encoding a nuclear protein that accelerates cell-cycle progression.

We herein describe a novel protein encoded by a single exon in a single-copy conserved mammalian gene. This protein, termed TMF regulated nuclear protein (TRNP), was identified in a yeast "two-hybrid" screen in which the "BC box" containing protein-TMF/ARA160 served as a bait. TRNP is a basic protein which accumulates in an insoluble nuclear fraction in mammalian cells. It is 227 aa long in humans and chimps and 223 aa long in mice. Enforced expression of TRNP in cells that do not express this protein significantly increased their proliferation rate by enhancing their cell-cycle progression from the G0/G1 to the S phase. Like another proliferation promoting factor, Stat3, TRNP was directed to proteasomal degradation by TMF/ ARA160. Thus, the trnp gene encodes a novel mammalian conserved nuclear protein that can accelerate cellcycle progression and is regulated by TMF/ARA160.

Fer kinase sustains the activation level of ERK1/2 and increases the production of VEGF in hypoxic cells.

Fer is a nuclear and cytoplasmic tyrosine kinase that is ubiquitously expressed in mammalian cells. Herein we show that Fer sustains a key signaling step in hypoxic cells. Knock-down of the Fer protein using a specific siRNA decreased the production of VEGF by the hypoxic cells. Conversely, ectopic expression of this kinase led to an elevated production of VEGF under hypoxia. At the molecular level, Fer was found to associate with ERK1/2 and this interaction was intensified under hypoxia. Moreover, Fer increased the activation levels of ERK1/2, and reducing the level of Fer, impaired the activation of ERK1/2 in hypoxic cells. Blocking the MEK-ERK1/2 signaling pathway with the MEK inhibitors U0126, or PD98059 led to the abrogation of ERK1/2 activity in hypoxic cells, an effect that was counteracted by Fer. Hence, Fer sustains the activation of ERK1/2 and increases the production of VEGF in hypoxic cells, without affecting the MEK-ERK signaling pathway.

Gamma interferon down-regulates Fer and induces its association with inactive Stat3 in colon carcinoma cells.

Gamma interferon (IFN-gamma) is a regulator of cell growth, which suppresses the proliferation of HT-29 colon carcinoma cells. Here we show that in HT-29 cells IFN-gamma transiently increased the cellular level of the tyrosine kinase Fer, whose functioning was found to be essential for the proliferation of malignant cell-lines. The transient elevation in the level of Fer, was followed by its down-regulation, an effect which was most prominent after 6-8 h of IFN-gamma treatment. Up- and down-regulation of Fer was paralleled by the activation and subsequent deactivation of Stat3, which is a potent oncogene and a putative substrate of the tyrosine kinase Fer. Moreover, IFN-gamma induced the association of Fer and Stat3 and the newly formed complex was most stable at the down-regulated states of the two proteins. Formation of the Fer/Stat3 complex was accompanied by an attenuation in cell-cycle progression and accumulation of cells in the G1 phase. Thus, Fer and Stat3 are two proliferation-promoting factors whose down-regulation could contribute to the cytostatic activity of IFN-gamma in colon carcinoma cells.