Specific interaction of type I receptors of the TGF-beta family with the immunophilin FKBP-12

Altered transforming growth factor signaling in epithelial cells when ras activation is blocked

We have previously demonstrated that growth inhibition of untransformed intestinal epithelial cells by transforming growth factor beta1 (TGFbeta) and TGFbeta2 was associated with a rapid activation of both Ras and extracellular signal-regulated kinase 1 (Erk1) (Mulder, K. M., and Morris, S. L. (1992) J. Biol. Chem. 267, 5029-5031; Hartsough, M. T., and Mulder, K. M. (1995) J. Biol. Chem. 270, 7117-7124). In order to determine whether Ras was required for TGFbeta regulation of both Erk1 and downstream components associated with TGFbeta-mediated growth inhibition, the intestinal epithelial cell (IEC) line IEC 4-1 was transfected with a vector containing a dominant-negative mutant of Ras (RasN17) under the control of an inducible metallothionein promoter. Using two different RasN17-transfected clones treated with ZnCl2, we demonstrate here that induction of Ras expression by at least 4-fold completely abrogated the TGFbeta-mediated activation of Erk1. Moreover, the RasN17-mediated reversal of the TGFbeta effect on Erk1 was dependent upon the level of expression of the dominant-negative protein. ZnCl2 treatment of control cells transfected with the empty vector did not alter Ras expression or the activation of Erk1 by TGFbeta. In order to determine whether the activation of Ras by TGFbeta was required for the growth inhibitory effect of TGFbeta, we examined TGFbeta2 effects on Cdk2-associated histone H1 kinase activity, cyclin A protein expression levels, and DNA synthesis in two intestinal epithelial cell clones transfected with RasN17. In cells expressing RasN17, we observed a 50% reversal of the inhibition of Cdk2 activity, a 78% reversal of the down-regulation of cyclin A protein expression, and a 21% reversal of the inhibition of DNA synthesis by TGFbeta. Collectively, these results indicate that Ras activation is obligatory for TGFbeta-mediated activation of Erk1, whereas it is partially required for the growth inhibitory effect of TGFbeta.

Characterization of the interaction of FKBP12 with the transforming growth factor-beta type I receptor in vivo

The type I transforming growth factor-beta receptor (TbetaR-I) is the efferent component of the receptor complex, which presumably phosphorylates intracellular targets. FKBP12, a binding protein for FK506 and rapamycin, is shown to associate with the cytoplasmic region of TbetaR-I in vitro. In this report, we investigated the interaction of FKBP12 with TbetaR-I in vivo. FKBP12 interacts with TbetaR-I in mammalian cells as well as in yeast. Ligand addition does not affect the interaction, and both constitutively active and kinase-negative mutants of TbetaR-I bind FKBP12. FKBP12 dissociates from TbetaR-I in the presence of a high concentration of FK506. The juxtamembrane region of TbetaR-I, containing the major phosphorylation sites by the type II receptor, is required for the interaction. One of the deletion mutants in this region, which was shown to mediate transcriptional response, does not bind FKBP12, suggesting that FKBP12 is not directly involved in TGF-beta signaling. Furthermore TbetaR-I does not phosphorylate FKBP12 in vitro. FKBP12 may not be a direct substrate of TbetaR-I but possibly modulates the TbetaR-I function through its interaction with the regulatory domain of the kinase.

Mammalian dwarfins are phosphorylated in response to transforming growth factor beta and are implicated in control of cell growth

The dwarfin protein family has been genetically implicated in transforming growth factor beta (TGF-beta)-like signaling pathways in Drosophila and Caenorhabditis elegans. To investigate the role of these proteins in mammalian signaling pathways, we have isolated and studied two murine dwarfins, dwarfin-A and dwarfin-C. Using antibodies against dwarfin-A and dwarfin-C, we show that these two dwarfins and an immunogenically related protein, presumably also a dwarfin, are phosphorylated in a time- and dose-dependent manner in response to TGF-beta. Bone morphogenetic protein 2, a TGF-beta superfamily ligand, induces phosphorylation of only the related dwarfin protein. Thus, TGF-beta superfamily members may use overlapping yet distinct dwarfins to mediate their intracellular signals. Furthermore, transient overexpression of either dwarfin-A or dwarfin-C causes growth arrest, implicating the dwarfins in growth regulation. This work provides strong biochemical and preliminary functional evidence that dwarfin-A and dwarfin-C represent prototypic members of a family of mammalian proteins that may serve as mediators of signaling pathways for TGF-beta superfamily members.

The immunophilin FKBP12 functions as a common inhibitor of the TGF beta family type I receptors

The immunophilin FKBP12 is an evolutionarily conserved abundant protein; however, its physiological roles remain poorly defined. Here we report that FKBP12 is a common cytoplasmic interactor of TGF beta family type I receptors. FKBP12 binds to ligand-free TGF beta type I receptor, from which it is released upon a ligand-induced, type II receptor mediated phosphorylation of the type I receptor. Blocking FKBP12/type I receptor interaction with FK506 nonfunctional derivatives enhances the ligand activity, indicating that FKBP12 binding is inhibitory to the signaling pathways of the TGF beta family ligands. Overexpression of a myristylated FKBP12 in Mv1Lu cell specifically inhibits two separate pathways activated by TGF beta, and two point mutations on FKBP12 (G89P, I90K) abolish the inhibitory activity of FKBP12, suggesting that FKBP12 may dock a cytoplasmic protein to the type I receptors to inhibit TGF beta family mediated signaling.

Serine phosphorylation, chromosomal localization, and transforming growth factor-beta signal transduction by human bsp-1

The transforming growth factor-beta (TGF-beta) superfamily regulates a multitude of cellular and developmental events. TGF-beta family ligands signal through transmembrane serine/threonine kinase receptors whose downstream effectors are largely unknown. Using genetic data from the fruit fly, we have identified a downstream effector of TGF-beta-induced signaling. TGF-beta signaling protein-1 (BSP-1) is rapidly phosphorylated in response to TGF-beta. Localization of bsp-1 to chromosome 4q28 suggests a role in carcinogenesis. These data suggest that BSP-1 is the prototype of a new class of signaling molecules.

Extracellular signal-regulated kinase and the small GTP-binding protein, Rac, contribute to the effects of transforming growth factor-beta1 on gene expression

The kinases and regulatory proteins that convey signals initiated by transforming growth factor-beta (TGF-beta) to the nucleus are poorly characterized. To study the role of the extracellular signal-regulated kinase (ERK) pathway in this process, we transiently transfected NIH 3T3 fibroblasts with TGF-beta-responsive luciferase reporter genes and expression vectors designed to interrupt this kinase cascade. Mitogen-activated protein (MAP) kinase phosphatase-1 and a dominant negative MAP/ERK kinase 1 mutant reduced stimulation of plasminogen activator inhibitor-1 (PAI-1) promoter activity by TGF-beta1 from 11.5- to 4-fold and 4.9-fold, respectively. Similar results were observed with the type I collagen promoters. TGF-beta1 increased ERK1 activity 4.5-fold at 5 min and 3. 1-fold at 3 h, while Jun kinase and p38 activity were not affected. Cotransfection of a dominant negative mutant of the small G protein, Rac, but not dominant negative Ras, Cdc42, or Rho mutants, reduced the effects of TGF-beta1 on the PAI-1 promoter by approximately half. In support of a role for Rac in signaling by TGF-beta, GTP binding to Rac was increased 3.7-fold following exposure of NIH 3T3 cells to TGF-beta1 for 3 min. These findings indicate that TGF-beta1 modulates gene expression partly through ERK and Rac in NIH 3T3 cells.

TGF beta 1 inhibits NF-kappa B/Rel activity inducing apoptosis of B cells: transcriptional activation of I kappa B alpha

TGF beta 1 treatment of B cell lymphomas decreases c-myc gene expression and induces apoptosis. Since we have demonstrated NF-kappa/Rel factors play a key role in transcriptional control of c-myc, we explored the effects of TGF beta1 on WEHI 231 immature B cells. A reduction in NF-kappa B/Rel activity followed TGF beta 1 treatment. In WEHI 231 and CH33 cells, we observed an increase in I kappa B alpha, a specific NF-kappa B/Rel inhibitor, due to transcriptional induction. Engagement of surface CD40 or ectopic c-Rel led to maintenance of NF-kappa B/Rel and c-Myc expression and protection of WEHI 231 cells from TGF beta 1-mediated apoptosis. Ectopic c-Myc expression overrode apoptosis induced by TGF beta 1. Thus, downmodulation of NF-kappa B/Rel reduces c-Myc expression, which leads to apoptosis in these immature B cell models of clonal deletion. The inhibition of NF-kappa B/Rel activity represents a novel TGF beta signaling mechanism.

Interaction of transforming growth factor-beta receptor I with farnesyl-protein transferase-alpha in yeast and mammalian cells

Transforming growth factor beta (TGF-beta) signals through two transmembrane serine/threonine kinases, known as TbetaR-I and TbetaR-II. Several lines of evidence suggest that TbetaR-II acts as a primary receptor, binding TGF-beta and phosphorylating TbetaR-I whose kinase activity then propagates the signal to unknown substrates. We report an interaction between TbetaR-I and the farnesyl-protein transferase-alpha subunit (FT-alpha) both in a yeast two-hybrid system and in mammalian cells. These findings raise the possibility that TGF-beta might regulate cellular functions by altering the ability of FT-alpha to catalyze isoprenylation of targets such as G proteins, lamins, or cytoskeletal components. However, we provide evidence that TGF-beta action does not alter the overall protein isoprenyl transferase activity in Mv1Lu mink lung epithelial cells. In fact, the beta subunits of farnesyl transferase and geranylgeranyl transferase, which are necessary for the activity of FT-alpha, prevent the association of FT-alpha with TbetaR-I. Furthermore, farnesyl transferase activity is shown to be dispensable for TGF-beta signaling of growth inhibitory and transcriptional responses in these cells. These results suggest that the interaction between TbetaR-I and FT-alpha does not affect the known functions of these two proteins.

Effects of rapamycin on ryanodine receptor/Ca(2+)-release channels from cardiac muscle

Ryanodine receptors (RyRs) are intracellular channels that regulate the release of Ca2+ from the endoplasmic reticulum of many cell types. The RyRs are physically associated with FK506-binding proteins (FKBPs); immunophilins, with cis-trans peptidyl-prolyl isomerase activity. FKBP12 copurifies with RyR1 (skeletal isoform) and modulates its gating. A different form of FKBP with a slightly higher molecular weight copurifies with RyR2 (cardiac isoform). Previous studies have demonstrated that FKBP stablizes gating of the skeletal Ca(2+)-release channel. In the present study, we measured the activity of cardiac RyRs incorporated into planar lipid bilayers to show that rapamycin, a drug that inhibits the prolyl isomerase activity of FKBP and dissociates FKBP from the RyR, increases the open probability and reduces the current amplitude of cardiac muscle Ca(2+)-release channels. These experiments show for the first time that submicromolar concentrations of rapamycin can alter channel function. Our results provide support for the hypotheses that FKBP functionally associates with the RyR and that the immunosuppressant drug, rapamycin, alters the function of both cardiac and skeletal muscle isoforms of the Ca(2+)-release channel. Our findings suggest that FKBP-dependent modulation of channel function may be generally applicable to all members of the intracellular Ca(2+)-release channel family and that FKBPs may play important regulatory roles in many cell processes, ranging from long-term depression in neurons to contractility in cardiomyocytes.

MADR1, a MAD-related protein that functions in BMP2 signaling pathways

Components of the signaling pathways that lie downstream of Ser/Thr kinase receptors and are required for signaling by the TGF beta superfamily have been poorly defined. The Drosophila gene Mothers against dpp (MAD) and the C. elegans sma genes are implicated in these signaling pathways. We show that MAD functions downstream of DPP receptors and is required for receptor signaling. Phosphorylation of MADR1, a human homolog of MAD, is tightly regulated and rapidly induced by BMP2, but not TGF beta or activin. This phosphorylation is necessary for function, since a point mutant that yields a null phenotype in Drosophila is not phosphorylated. BMP2 treatment results in accumulation of MADR1 in the nucleus. MAD proteins may thus define a novel class of signaling molecules with nuclear function in Ser/Thr kinase receptor signaling pathways.

Xenopus Mad proteins transduce distinct subsets of signals for the TGF beta superfamily

Xenopus cDNAs homologous to the Drosophila Mad gene and C. elegans CEM genes have been cloned and functionally analyzed by microinjection into frog embryos. The results show that these genes (Xmad) encode intracellular proteins that act downstream of TGF beta superfamily ligands. Most interesting is the fact that different Xmad proteins produce distinct biological responses. Xmad1 produces ventral mesoderm, apparently transducing a signal for BMP2 and BMP4, whereas Xmad2 induces dorsal mesoderm like Vg1, activin, and nodal. These results suggest that an individual Xmad protein waits poised in the cytoplasm for instruction from a distinct subset of TGF beta ligands and then conveys specific information to the nucleus.

Purification and characterization of cytosolic and microsomal cyclophilins from maize (Zea mays)

Methods for the purification and separation of peptidyl prolyl cis-trans isomerase (PPI) from cytosolic and microsomal fractions of etiolated maize are described. On SDS/PAGE, the purified preparations appears as single polypeptides with molecular masses of 17.5 kDa and 17.7 kDa respectively. Instead of using immobilized cyclosporin A derivatives as affinity adsorbents, our methods employ conventional techniques enabling purification of the proteins on a much larger scale than previously described. An antiserum raised against the cytosolic PPI recognizes polypeptides of similar molecular mass from a wide range of plant species on an immunoblot. There is virtually no recognition of the microsomal PPI. The cytosolic and microsomal PPIs are inhibited by cyclosporin A (Ki = 6 nM in both cases), indicating that they are cyclophilins. The cytosolic enzyme is inactivated by 5 mM N-ethylmaleimide and 2 mM phenylglyoxal. N-terminal sequencing of the microsomal PPI indicates a high level of sequence similarity with the N-terminal sequence of mature animal s-cyclophilin (cyclophilin B).

Transforming Growth Factor-beta Receptors: Role in Physiology and Disease

Transforming growth factor-beta (TGF-beta) plays a pivotal role in numerous vital cellular activities, most significantly the regulation of cellular proliferation and differentiation and synthesis of extracellular matrix components. Its ubiquitous presence in different tissues and strict conservation of nucleotide sequence down through the most primitive vertebrate organism underscore the essential nature of this family of molecules. The effects of TGF-beta are mediated by a family of dedicated receptors, the TGF-beta types I, II, and III receptors. It is now known that a wide variety of human pathology can be caused by aberrant expression and function of these receptors or their cognate ligands. The coding sequence of the human type II receptor appears to render it uniquely susceptible to DNA replication errors in the course of normal cell division. There are now substantial data suggesting that TGF-beta type II receptor should be considered a tumor suppressor gene. High levels of mutation in the TGF-beta type II receptor gene have been observed in a wide variety of primarily epithelial malignancies, including colon, gastric, and hepatic cancer. It appears likely that mutation of the TGF-beta type II receptor gene represents a very critical step in the pathway of carcinogenesis. Copyright 1996 S. Karger AG, Basel

Multiple cis-trans conformers of the prolactin receptor proline-rich motif (PRM) peptide detected by reverse-phase HPLC, CD and NMR spectroscopy

An eight-amino-acid synthetic peptide (IIe1-Phe2-Pro3-Pro4-Val5-Pro6-Gly7-Pro8) corresponding to the conserved proline-rich motif (PRM) of the intracellular domain of the prolactin receptor (PRL-R) was studied by one- and two-dimensional (1D and 2D) proton NMR spectroscopy in water and DMSO in order to characterize its conformational dynamics. The purified PRL-R PRM peptide eluted as two partially resolved peaks in equilibrium on reverse-phase HPLC (RP-HPLC) at 20 degrees C with a ratio of 60:40. At 30 degrees C, the two peaks coalesced into a single peak The two RP-HPLC peaks correspond to two peptide conformers resulting from the slow cis-trans isomerization of one of the four proline amide bonds. Although the peptide has only three amide (NH) protons, its ID NMR spectrum in water contains approximately 15 discernible NH region peaks, providing evidence for multiple conformers. The amide resonances were assigned on the basis of 2D-COSY spectra, chemical shift values resonance splitting patterns and temperature coefficients. The cis:trans ratio for each proline in water, calculated from integrated intensities and/or peak heights of the appropriate resonances, were Phe2-Pro3 (35:65), Pro3-Pro4 (40:60), Val5-Pro6 (70:30), and Gly7-Pro8 (30:70). Temperature studies (25-70 degrees C) were used to semi-quantitatively estimate the rates of isomerization for the different prolines. In water, Pro8 undergoes rapid isomerization; Pro3 isomerizes at an intermediate rate; while Pro4 and Pro6 both appear to isomerize very slowly since no coalescence of amide resonances was observed. In DMSO, only Pro4 displayed slow isomerization. Slow kinetics combined with a similar 60:40 ratio of conformers determined by RP-HPLC and NMR suggests that isomerization of the Pro3-Pro4 bond generates the two RP-HPLC peaks. Both proximal and distal proline isomerization effects were observed in NMR experiments. All of the 16 theoretical (24 = 16) proline configurations appear to exist in equilibrium in water The predominant (19%) conformation, trans3-trans4-cis6-trans8, may reflect the configuration of the PRM prolines in the native PRL-R. Isomerization of Pro6 from cis to trans generates an interaction between the peptide N-and C-termini, suggesting an overall pseudo-cyclic conformation. This all-trans proline configuration may play an important biochemical role in the function of cytokine/haematopoietin receptors. A model is proposed which suggests that isomerization of the PRM by an immunophilin such as the FK 506-binding protein (FKBP) serves as an on-off switch for cytokine receptor activation.

Signaling via hetero-oligomeric complexes of type I and type II serine/threonine kinase receptors

Members of the transforming growth factor-beta (TGF-beta) superfamily have been found to signal by inducing the formation of hetero-oligomeric complexes of different type I and type II serine/threonine kinase receptors. Recent data indicate that binding of TGF-beta to its constitutively active type II receptor recruits the type I receptor into the complex; the type I receptor is thereafter phosphorylated and activated, processes which are necessary and sufficient for most TGF-beta mediated responses. Recent genetic analyses of Drosophila also indicate a strict requirement for both type I and type II receptors in decapentaplegic signaling in vivo.

Growth factor and sex steroid interactions in breast cancer

Mitogenic and inhibitory growth factors and steroid ovarian hormones play important roles as selective modulators of normal mammary development and in the onset and the progression of human breast cancer. The focus of this article is to review past and current research on the interactions of these two classes of effectors in mammary gland development and neoplasia. Steroid hormones regulate synthesis of growth stimulatory and inhibitory growth factors, growth factor receptors, and growth factor binding proteins. In turn, growth factor pathways may modulate phosphorylation and function of steroid receptors and potentiate or inhibit the mitogenic actions of steroids. Ultimately, during the progression of the malignant mammary epithelial cell to hormonal autonomy, overexpression, mutation, or disregulation of key elements of growth factor signal transduction pathways all may play critical roles.

Regulation and interactions of transforming growth factor-beta with cardiovascular cells: implications for development and disease

1. Transforming growth factors-beta (TGF-beta) are multifunctional proteins that regulate cell growth, differentiation, migration and extracellular matrix production and have an important role in embryonic development and tissue remodelling. 2. The diverse biological actions of TGF-beta are elicited following their interaction with type I and type II TGF-beta receptors, both of which are transmembrane serine/threonine kinases, suggesting an important role for protein phosphorylation in the mechanism of action of these cytokines on the growth of cells and their extracellular environment. 3. Alterations in TGF-beta gene expression and action in various cell types associated with the cardiovascular system may contribute to the pathophysiology of a number of diseases, such as hypertension, atherosclerosis and restenosis, as well as the development of cardiac abnormalities.

Immunosuppressants and TGF-beta 1 accelerated and prolonged the nitric oxide/oxyradicals-dependent suppression by dexamethasone in paw edema of mice

Dexamethasone (Dex, 0.3 mg/kg, s.c.) did not suppress histamine and ischemic paw edema of mice up to 1 hr. However, given TGF-beta 1 (0.3 microgram/kg, i.p.), Dex suppression appeared early as 30 min (36% and 42%). When Dex (0.1 mg/kg, s.c.) was injected 6 hr before the assay, Dex alone, TGF-beta 1 +/- Dex, FK506 (10 mg/kg, oral) +/- Dex, cyclosporin (CsA, 30 mg/kg, oral) +/- Dex, rapamycin (Rapa, 10 mg/kg, i.p.) +/- Dex, deoxyspergualin (DSP, 10 mg/kg, i.p.) +/- Dex, did not suppress the edemata (less than 11%). Nevertheless, if Dex and TGF-beta 1 were dosed together with one of these immunosuppressants, suppressions of histamine and ischemic edema were 53%, 45% (FK506), 45%, 49% (CsA), 44%, 48% (Rapa) and 39%, 51% (DSP), respectively. Glucocorticoid (GC) receptor (GR) complex contains heat shock proteins such as hsp56 (or CsA-binding protein: CyP-40), hsp70 and hsp90. FK506, Rapa and TGF-beta 1 receptor I (TR-I) bind FK-binding protein-12 (FKBP-12). FK506 and Rapa bind also hsp56. CsA binds CyP-40. DSP binds hsp70 and/or hsp90. These bindings might change or stabilize the conformation of GR complex resulting in edema suppressions. Nitric oxide synthase (NOS) inhibitors, superoxide dismutase (SOD), catalase, mannitol and cycloheximide, reversed the edema suppressions by TGF-beta1 +/- immunosuppressant at 30 min and 6 hr after Dex. Endogenous NO, O2- and/or .OH seemed to be essential for edema suppressions. Our demonstration in vivo may offer a theoretical support for clinicians to adopt combination therapy of immunosuppressant(s) and GC.

The p21(RAS) farnesyltransferase alpha subunit in TGF-beta and activin signaling

The alpha subunit of p21(RAS) farnesyltransferase (FNTA), which is also shared by geranylgeranyltransferase, was isolated as a specific cytoplasmic interactor of the transforming growth factor-beta (TGF-beta) and activin type I receptors with the use of the yeast two-hybrid system. FNTA interacts specifically with ligand-free TGF-beta type l receptor but is phosphorylated and released upon ligand binding. Furthermore, the release is dependent on the kinase activity of the TGF-beta type II receptor. Thus, the growth inhibitory and differentiative pathways activated by TGF-beta and activin involve novel mechanisms of serine-threonine receptor phosphorylation-dependent release of cytoplasmic interactors and regulation of the activation of small G proteins, such as p21(RAS).

Identification of a nuclear-specific cyclophilin which interacts with the proteinase inhibitor eglin c

We have identified a novel human cyclophilin (hCyP-60) which interacts with the proteinase inhibitor eglin c using the yeast two-hybrid system. A cDNA isolated from a Raji B lymphocyte library reveals a domain showing sequence similarity to known cyclophilins flanked by unique N- and C-terminal residues. In addition, hCyP-60 contains a tyrosine residue (Tyr 389) instead of a tryptophan residue found in most eukaryotic cyclophilins at a position important for cyclosporin binding. Northern and Western analysis reveal widespread expression with considerable tissue-specific variation. Specifically, the highest levels of mRNA are detected in the thymus, pancreas, testis, and K-562 cell line, while the most protein is detected in the kidney. Immunohistochemistry indicates a nuclear-specific localization both in transfected cells and tissue sections. hCyP-60's specific subcellular localization and conserved amino acid sequence suggest that it may play a specific role in the nucleus.

Reduction of epidermal growth factor receptor phosphorylation by activated Mullerian inhibiting substance is vanadate-sensitive

The carboxy-terminal domain of recombinant human Mullerian inhibiting substance (MIS) inhibits cellular proliferation in vitro and decreases epidermal growth factor (EGF)-dependent phosphorylation of the EGF receptor. Proteolytically cleaved and undissociated MIS is more potent than carboxy-terminal MIS alone, supporting a functional role for the amino-terminal region of the molecule. MIS does not block EGF binding to the EGF receptor, thus, MIS reduction of EGF receptor phosphorylation must occur distal to receptor ligand binding. The effect of proteolytically cleaved MIS on reduction of EGF receptor phosphorylation in membrane preparations is decreased by a specific phosphatase inhibitor, vanadate, thus implicating a membrane phosphatase in this MIS action at the EGF receptor.

Transforming growth factor-beta system and its regulation by members of the steroid-thyroid hormone superfamily

TGF-beta s and their receptors are expressed ubiquitously, and they act as key regulators of many aspects of cell growth, differentiation, and function. Steroid action on target tissues is often associated with increase in TGF-beta isoforms. Regulation of TGF-beta expression and activation is crucial for normal development and growth control. The loss of responsiveness of different tumor cells to the antiproliferative effects of TGF-beta is a common feature in carcinogenesis. Multiple changes are required for the cells to gain complete resistance to TGF-beta growth inhibition (Fynan and Reiss, 1993; Kimchi et al., 1988; Samuel et al., 1992). Although many tumor cells are not growth inhibited by TGF-beta, they respond to TGF-beta treatment by changes in the expression of matrix components and enhanced proteolytic activity (KeskiOja et al., 1988). Agents that induce TGF-beta production in target tissues can have a chemopreventive or chemotherapeutic value for the management of epithelial malignancies. Conversely, data supporting a positive role for TGF-beta in established tumor progression are beginning to emerge (Arteaga et al., 1993a,b; Barrett-Lee et al., 1990; Arrick et al., 1992 ; E. A. Thompson et al., 1991). In later stages of tumor development, cell proliferation is often not inhibited by TGF-beta, and tumor cells secrete large amounts of this growth factor (Fynan and Reiss, 1993). In vivo TGF-beta secreted by tumor or stromal cells can influence host responses such as a natural killer cell function and thus indirctly support tumor cell viability (Arteaga et al., 1993b). TGF-beta may also affect tumor growth indirectly by stromal effects and promotion of angiogenesis. TGF-beta may also be involved in the progression of breast tumors from the steroid-sensitive to steroid-insensitive state (King et al., 1989). Understanding of the net effect of TGF-beta in different stages of tumor development is critical for the evaluation of its therapeutic value in cancer treatment.

Interaction of the transforming growth factor-beta type I receptor with farnesyl-protein transferase-alpha

Transforming growth factor-beta 1 (TGF-beta 1) is the prototype of a large family of molecules that regulate a variety of biological processes. The type I (T beta R-I) and type II (T beta R-II) receptors for TGF-beta 1 are transmembrane serine/threonine kinases, forming a heteromeric signaling complex. Recent studies have shown that T beta R-II is a constitutively active kinase and phosphorylates T beta R-I upon ligand binding, suggesting that T beta R-I is the effector subunit of the receptor complex, which transduces signals to intracellular targets. This model has been further confirmed by the identification of constitutively active T beta R-I that mediates TGF-beta 1-specific cellular responses in the absence of ligand and T beta R-II. To investigate signaling by TGF-beta 1, we have sought to isolate proteins that interact with the cytoplasmic region of T beta R-I. One of the proteins identified was the alpha subunit of farnesyl-protein transferase (FT alpha) that modifies a series of peptides including Ras. T beta R-I specifically interacts with FT alpha in the yeast two-hybrid system. Glutathione S-transferase-T beta R-I fusion proteins bind FT alpha translated in vitro. T beta R-I also phosphorylates FT alpha. We further show that the constitutively active T beta R-I interacted with FT alpha very strongly whereas an inactive form of T beta R-I did not. These results suggest that FT alpha may be one of the substrates of the activated T beta R-I kinase.

Mechanism of action of the immunosuppressant rapamycin

Rapamycin has potent immunosuppressive properties reflecting its ability to disrupt cytokine signaling that promotes lymphocyte growth and differentiation. In IL-2-stimulated T cells, rapamycin impedes progression through the G1/S transition of the proliferation cycle, resulting in a mid-to-late G1 arrest. Two major biochemical alterations underlie this mode of action. The first one affects the phosphorylation/activation of the p70 S6 kinase (p70s6k), an early event of cytokine-induced mitogenic response. By inhibiting this enzyme, whose major substrate is the 40S ribosomal subunit S6 protein, rapamycin reduces the translation of certain mRNA encoding for ribosomal proteins and elongation factors, thereby decreasing protein synthesis. A second, later effect of rapamycin in IL-2-stimulated T cells is an inhibition of the enzymatic activity of the cyclin-dependent kinase cdk2-cyclin E complex, which functions as a crucial regulator of G1/S transition. This inhibition results from a prevention of the decline of the p27 cdk inhibitor, that normally follows IL-2 stimulation. To mediate these biochemical alterations, rapamycin needs to bind to intracellular proteins, termed FKBP, thereby forming a unique effector molecular complex. However, neither(p70s6k) inhibition, nor p27-induced cdk2-cyclin E inhibition are directly caused by the FKBP-rapamycin complex. Instead, this complex physically interacts with a novel protein, designated "mammalian target of rapamycin" (mTOR), which has sequence homology with the catalytic domain of phosphatidylinositol kinases and may therefore be itself a kinase. mTOR may act upstream of (p70s6K) and cdk2-cyclin E in a linear or bifurcated pathway of growth regulation. Molecular dissection of this pathway should further unravel cytokine-mediated signaling processes and help devise new immunosuppressants.

Transmembrane signaling in kidney health and disease

Transmembrane signal transduction is the process whereby a ligand binds to the external surface of the cell membrane and elicits a physiological response specific for that ligand and cell type. It is now appreciated that numerous disease states represent disturbances in normal transmembrane signaling mechanisms. In the current paper, we focus our attention on the mesangial cell of the glomerular microcirculation as a prototypical model system for understanding normal and abnormal transmembrane signaling processes. Among the major receptor and effector mechanisms for transmembrane signal transduction in the mesangial cell, this paper emphasizes the phospholipase effector response to growth factors and vasoactive hormones. The post-translational and transcriptional pathways for regulation of phospholipase C and phospholipase A2 are described, including consideration of perturbations in these systems that characterize two disease models, namely: acute cyclosporine nephrotoxicity and early diabetic glomerulopathy.

Human type II receptor for bone morphogenic proteins (BMPs): extension of the two-kinase receptor model to the BMPs

Bone morphogenic proteins (BMPs) are universal regulators of animal development. We report the identification and cloning of the BMP type II receptor (BMPR-II), a missing component of this receptor system in vertebrates. BMPR-II is a transmembrane serine/threonine kinase that binds BMP-2 and BMP-7 in association with multiple type I receptors, including BMPR-IA/Brk1, BMPR-IB, and ActR-I, which is also an activin type I receptor. Cloning of BMPR-II resulted from a strong interaction of its cytoplasmic domain with diverse transforming growth factor beta family type I receptor cytoplasmic domains in a yeast two-hybrid system. In mammalian cells, however, the interaction of BMPR-II is restricted to BMP type I receptors and is ligand dependent. BMPR-II binds BMP-2 and -7 on its own, but binding is enhanced by coexpression of type I BMP receptors. BMP-2 and BMP-7 can induce a transcriptional response when added to cells coexpressing ActR-I and BMPR-II but not to cells expressing either receptor alone. The kinase activity of both receptors is essential for signaling. Thus, despite their ability to bind to type I and II receptors receptors separately, BMPs appear to require the cooperation of these two receptors for optimal binding and for signal transduction. The combinatorial nature of these receptors and their capacity to crosstalk with the activin receptor system may underlie the multifunctional nature of their ligands.

Cyclophilin A and FKBP12 interact with YY1 and alter its transcriptional activity

YY1 is a zinc finger transcription factor with unusual structural and functional features. In a yeast two-hybrid screen, two cellular proteins, cyclophilin A (CyPA) and FK506-binding protein 12 (FKBP12), interacted with YY1. These interactions are specific and also occur in mammalian cells. Cyclosporin A and FK506 efficiently disrupt the YY1-CyPA and YY1-FKBP12 interactions. Overexpression of human CyPA and FKBP12 have different effects on YY1-regulated transcription with these effects being promoter-dependent. These results suggest that immunophilins may be mediators in the functional role of YY1.

Cytokines regulate the cellular phenotype of developing neural lineage species

The patterns and mechanisms of action of inductive signals that orchestrate neural lineage commitment and differentiation in the mammalian brain are incompletely understood. To examine these developmental issues, we have utilized several culture systems including conditionally immortalized cell lines, subventricular zone progenitor cells and primary neuronal cultures. A neural stem and progenitor cell line (MK31) was established from murine embryonic hippocampus by retroviral transduction of temperature-sensitive alleles of the simian virus 40 large tumor antigen. At the non-permissive temperature for antigen expression (39 degrees C) in serum-free media, the neural stem cells give rise to a series of increasingly mature neuronal progenitor and differentiated cellular forms under the influence of a subset of hematolymphopoietic cytokines (interleukins 5, 7, 9 and 11), when individually co-applied with transforming growth factor alpha, after pretreatment with basic fibroblast growth factor. These cellular forms elaborated a series of progressively more mature neurofilament proteins, a sequential pattern of ligand-gated channels, and inward currents and generation of action potentials with mature physiological properties. Because the factors regulating the development of central nervous system astrocytes have been so difficult to define, we have chosen to focus, in this manuscript, on the elaboration of this cell type. At 39 degrees C, application of a subfamily of bone morphogenetic proteins of the transforming growth factor beta superfamily of growth factors sanctioned the selective expression of astrocytic progenitor cells and mature astrocytes, as defined by sequential elaboration of the Yb subunit of glutathione-S-transferase and glial fibrillary acidic protein. These lineage-specific cytokine inductive relationships were verified using subventricular zone neural progenitor cells generated by the application of epidermal growth factor, alone or in combination with basic fibroblast growth factor, to dissociated cellular cultures derived from early embryonic murine brain, a normal non-transformed developmental population. Finally, application of a different series of cytokines from five distinct factor classes (basic fibroblast growth factor, platelet-derived growth factor-AA, insulin-like growth factor 1, neurotrophin 3 and representative gp130 receptor subunit-related ligands) caused the elaboration of oligodendroglial progenitor species and post-mitotic oligodendrocytes, defined by progressive morphological maturation and the expression of increasingly advanced oligodendroglial and oligodendrocyte lineage markers. In addition, seven different gp130-associated neuropoietic (ciliary neurotrophic factor, leukemia inhibitory factor, oncostatin-M) and hematopoietic (interleukins 6, 11, 12, granulocyte-colony stimulating factor) cytokines exhibited differential trophic effects on oligodendroglial lineage maturation and factor class interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of Ca2+ signaling in neutrophils by the mast cell-released immunophilin FKBP12

The immunophilins of the FK506-binding protein (FKBP) family are intracellular proteins that bind the immunosuppresants FK506 and rapamycin. In this study we show that HMC-1 mast cells sensitized with IgE release FKBP12 upon stimulation with anti-IgE. The release is rapid and not affected by actinomycin D or cycloheximide, suggesting that it is due to exocytosis from a storage compartment. FKBP12 from HMC-1 mast cells exhibits biological activity. When applied extracellularly to human neutrophils, it induces transient changes in the intracellular Ca2+ concentration ([Ca2+]i) due to Ca2+ release from intracellular stores. Inhibition of [Ca2+]i changes by ruthenium red and ryanodine indicates that ryanodine receptor/Ca2+ release channels are involved in FKBP12-induced Ca2+ signaling. Neutrophil activation by mast cell-derived FKBP12 is prevented by complexing FKBP12 with FK506 or rapamycin. These results demonstrate that extracellular FKBP12 functions as a cytokine in cell-to-cell communication. They further suggest a pathophysiological role for FKBP12 as a mediator in immediate or type I hypersensitivity and may have implications for novel therapeutic strategies in the treatment of allergic disorders with FK506 and rapamycin.

Transforming growth factor beta activation of p44mapk in proliferating cultures of epithelial cells

Transforming growth factor-beta (TGF-beta) is a potent growth inhibitor of a variety of epithelial cell types. The primary signaling mechanism involved in mediating this and other cellular effects of TGF-beta is still unknown. We report here that both TGF-beta 1 and TGF-beta 2 resulted in a rapid activation of mitogen-activated protein kinase (MAPK) p44mapk, occurring within 5-10 min of growth factor addition. This effect occurred in exponentially proliferating cultures of intestinal epithelial (IEC) 4-1 cells under conditions in which DNA synthesis was inhibited by 95% to 98%. Furthermore, TGF-beta 2 induced a sustained activation of p44mapk under these conditions, lasting for at least 90 min after initial growth factor treatment. Another TGF-beta-sensitive epithelial cell line (CCL 64) displayed a similar rapid increase in p44mapk activity when treated with TGF-beta 1. In contrast, in IEC 4-6 cells that are resistant to TGF-beta effects on growth and DNA synthesis, TGF-beta 2 treatment did not result in an activation of p44mapk. In contrast to the results in proliferating cultures, treatment of quiescent cultures of IEC 4-1 cells with TGF-beta 2 resulted in no significant change in either DNA synthesis or p44mapk activity within 15 min of TGF-beta addition. In contrast, addition of the growth-stimulatory combination of factors (epidermal growth factor + insulin + transferrin = EIT) to quiescent and proliferating IEC 4-1 cells stimulated DNA synthesis and resulted in a sustained activation of p44mapk. Together, our results suggest an association between activation of p44mapk and both TGF-beta-mediated growth inhibition and EIT-mediated growth stimulation. This suggests that the specificity for the cellular effects of growth factors may not occur at the level of MAPK activation per se, but rather at downstream events that include phosphorylation of distinct transcriptional complexes and activation of a select assortment of genes. With regard to TGF-beta specifically, we have proposed a model to explain how activation of p44mapk may be associated with a growth-inhibitory response.

Immunophilin FK506 binding protein associated with inositol 1,4,5-trisphosphate receptor modulates calcium flux

The immunophilin FK506 binding protein 12 (FKBP12) is associated with and modulates the ryanodine receptor calcium release channel of skeletal muscle. Ryanodine receptor has amino acid homology and functional similarity with another intracellular Ca2+ release channel, the inositol 1,4,5-trisphosphate receptor (IP3R). In the present study we show that highly purified preparations of IP3R contain FKBP12. The complex of these two proteins is disrupted by the immunosuppressants FK506 and rapamycin, both of which are known to bind FKBP12 with high affinity. Disrupting the IP3R-FKBP12 interaction increases Ca2+ flux through IP3R, an effect that is reversed by added FKBP12. FKBP12 appears to be physiologically linked to IP3R, regulating its Ca2+ conductance.

Characterization of an exchange reaction between soluble FKBP-12 and the FKBP.ryanodine receptor complex. Modulation by FKBP mutants deficient in peptidyl-prolyl isomerase activity

FKBP-12 (FKBP), the soluble receptor for the immunosuppresant drug FK-506, is tightly bound to the calcium release channel (CRC)/ryanodine receptor (RyR) of skeletal muscle terminal cisternae (TC) of sarcoplasmic reticulum with a stoichiometry of 4 mol of FKBP per tetrameric RyR complex. FKBP displays cis/trans-peptidyl-prolyl isomerase (PPIase) activity which is inhibited by FK-590 or rapamycin. In skeletal muscle TC, FK-590 or rapamycin binds to and dissociates FKBP from the RyR in a time- and temperature-dependent manner which increases the open probability of the channel. Therefore, the net energized Ca2+ uptake rate of TC vesicles devoid of FKBP is reduced due to the increased leak of Ca2+ from the TC specifically via the RyR, which is reversed upon rebinding of FKBP. Thus, the RyR is modulated by FKBP (Timerman, A. P., Ogunbumni, E., Freund, E. A., Wiederrecht, G., Marks, A. R., and Fleischer, S. (1993) J. Biol. Chem. 268, 22922-22999; Mayrleitner, M., Timerman, A. P., Wiederrecht, G., and Fleischer S. (1994) Cell Calcium 15, 99-108). We now find that FKBP can be displaced from the FKBP.RyR complex by exchange with FKBP in solution. The EC50 for exchange is 0.30 microM for wild type FKBP versus 0.6 to 2.4 microM for three different site-directed mutants that are practically devoid of any measurable PPIase activity. Substitution of wild-type FKBP on the RyR complex with these PPIase-deficient mutants did not alter the Ca2+ flux of TC vesicles, whereas dissociation of FKBP from TC with FK-590 increased the Ca2+ leak rate. Our studies show that, in vivo, the FKBP.RyR complex is in equilibrium with the cytosolic pool of FKBP (approximately 3 microM) and suggest that modulation of the CRC by FKBP is independent of PPIase activity.

Immunophilins and the nervous system

The search for immunosuppressant drugs to increase the success of organ transplantation led to the discovery of the immunophilins, proteins that interface with a range of signal transduction systems inside cells, especially in the nervous and immune systems. Here we review how these interesting molecules work and consider their therapeutic potential.

Nucleolar proteins that bind NLSs: a role in nuclear import or ribosome biogenesis?

In a search for proteins that bind nuclear localization sequences (NLSs), a number of nucleolar proteins with diverse functions were found. It is thought that the assay fortuitously uncovered a novel domain that mediates the interaction between these nucleolar proteins and ribosomal proteins containing NLS-like sequences. The domain is highly acidic and contains a number of serines forming putative casein kinase II sites. Here, we propose a model in which the nucleolar proteins catalyse the assembly of ribosomal proteins with pre-rRNA.

TGF-beta-receptor-mediated signaling

Transforming growth factor beta (TGF-beta) and its many relatives are thought to play key roles in the control of cell proliferation and differentiation. In particular, the ability of TGF-beta to induce growth arrest in epithelial cells has drawn considerable attention. The recent cloning of TGF-beta receptors, which are considered to be prototypes of a new class of cell-surface receptors, has provided a first insight into how TGF-beta signaling induces a variety of intracellular changes. Furthermore, recent advances in the characterization of the cell-cycle machinery have stimulated studies aimed at understanding how TGF-beta signaling leads to growth arrest in the late G1 phase of the cell cycle.

Developmental signalling. Sorting out the signals

New insights into the developmental roles played by the TGF-beta family of signalling molecules come from the identification in Drosophila of two transmembrane receptors encoded by the thick veins and saxophone genes.

Effects of transforming growth factor beta 1 on the adenylyl cyclase-cAMP pathway in prostate cancer

We reported previously that MATLyLu rat prostate cancer cells engineered to overproduce transforming growth factor beta 1 (TGF beta 1) produce larger, more metastatic tumors in vivo. We recognized that this ability of TGF beta 1 to act as a positive modulator of prostate tumor behavior might be due to effects of TGF beta 1 on the host and/or on the tumor cells. In this study we demonstrated that the cells themselves respond to endogenously produced TGF beta 1, and that the adenylyl cyclase (AC)-cAMP pathway is affected. TGF beta 1-overproducing cells had lower membrane AC activity, lower intracellular cAMP content, and a lower Gs alpha protein level than did control cells. Prostate cancer cells were growth inhibited by 8-bromo-cAMP or forskolin, agents that elevate intracellular cAMP. Thus, TGF beta 1 overproduction affects the phenotype of the tumor cells, deliberate activation of endogenously produced latent TGF beta 1 is not required (indicating that the cells themselves are capable of activating latent TGF beta 1), and TGF beta 1 overproduction lowers the cellular concentration of the growth inhibitor cAMP. Therefore, TGF beta 1 overproduction could affect tumor behavior in vivo in part via a direct effect on the tumor cells.