Constitutive expression of the Pim-1 kinase prolongs survival of cytokine-deprived FDCP1 cells, partly via maintenance of Bcl-2 expression. Here, we show that Pim-1 colocalizes and physically interacts with the pro-apoptotic Bad protein and phosphorylates it in vitro on serine 112, which is a gatekeeper site for its inactivation. Furthermore, wild-type Pim-1, but not a kinase-deficient mutant, enhances phosphorylation of this site in FDCP1 cells and protects cells from the pro-apoptotic effects of Bad. Our results suggest that phosphorylation of Bad by Pim-1 is one of several mechanisms via which the Pim-1 kinase can enhance Bcl-2 activity and promote cell survival.

Hematopoietic growth factors mediate the survival and proliferation of blood-forming cells, but the mechanisms through which these proteins produce their effects are incompletely known. Recent studies have identified the pim family of kinases as mediators of cytokinedependent survival signals. Several studies have identified substrates for the pim-1 kinase, but little is known about the other family members, pim-2 and pim-3. We have investigated potential functions for the pim-2 kinase in factor-dependent murine hematopoietic cells. We find that pim-2 mRNA and protein expression are regulated by cytokines similarly to pim-1. Three PIM-2 protein isoforms are produced in cytokinetreated cells. All three forms are active kinases, and the short (PIM-2(34 kDa)) form is the most active at enhancing survival of FDCP1 cells after cytokine withdrawal. This pro-survival function involves inhibition of apoptosis and caspase activation. Enforced expression of PIM-2(34 kDa) kinase does not appear to regulate expression of BCL-2, BCL-xL, BIM, or BAX proteins. However, the kinase can phosphorylate the pro-apoptotic protein BAD on serine 112, which accounts in part for its ability to reverse Bad-induced cell death. Our results indicate that pim-2 functions similarly to pim-1 as a pro-survival kinase and suggest that BAD is a legitimate PIM-2 substrate.

The pim-1 oncogene is regulated by hematopoietic cytokine receptors, encodes a serine/threonine protein kinase, and cooperates with c-myc in lymphoid cell transformation. Using a yeast two-hybrid screen, we found that Pim-1 protein binds to p100, a transcriptional coactivator that interacts with the c-Myb transcription factor. Pim-1 phosphorylated p100 in vitro, formed a stable complex with p100 in animal cells, and functioned downstream of Ras to stimulate c-Myb transcriptional activity in a p100-dependent manner. Thus, Pim-1 and p100 appear to be components of a novel signal transduction pathway affecting c-Myb activity, linking all three to the cytokine-regulated control of hematopoietic cell growth, differentiation, and apoptosis.

The basic helix‐loop‐helix‐leucine zipper (bHLHZip) protein Max associates with members of the Myc family, as well as with the related proteins Mad (Mad1) and Mxi1. Whereas both Myc:Max and Mad:Max heterodimers bind related E‐box sequences, Myc:Max activates transcription and promotes proliferation while Mad:Max represses transcription and suppresses Myc dependent transformation. Here we report the identification and characterization of two novel Mad1‐ and Mxi1‐related proteins, Mad3 and Mad4. Mad3 and Mad4 interact with both Max and mSin3 and repress transcription from a promoter containing CACGTG binding sites. Using a rat embryo fibroblast transformation assay, we show that both Mad3 and Mad4 inhibit c‐Myc dependent cell transformation. An examination of the expression patterns of all mad genes during murine embryogenesis reveals that mad1, mad3 and mad4 are expressed primarily in growth‐arrested differentiating cells. mxi1 is also expressed in differentiating cells, but is co‐expressed with either c‐myc, N‐myc, or both in proliferating cells of the developing central nervous system and the epidermis. In the developing central nervous system and epidermis, downregulation of myc genes occurs concomitant with upregulation of mad family genes. These expression patterns, together with the demonstrated ability of Mad family proteins to interfere with the proliferation promoting activities of Myc, suggest that the regulated expression of Myc and Mad family proteins function in a concerted fashion to regulate cell growth in differentiating tissues.

The aim of this study was to identify whey-derived peptides with angiotensin I-converting enzyme (ACE) inhibitory activity. The bovine whey proteins α-lactalbumin and β-lactoglobulin were hydrolysed with pepsin, trypsin, chymotrypsin, pancreatin, elastase or carboxypeptidase alone and in combination. The total hydrolysates were fractionated in a two step ultrafiltration process, first with a 30 kDa membrane and then with a 1 kDa membrane. Inhibition of ACE was analysed spectrophotometrically. The peptides were isolated by chromatography and identified by mass and sequencing analysis. The most potent inhibitory peptides were synthesized by the 9-fluorenylmethoxycarbonyl solid phase method. Inhibition of ACE was observed after hydrolysis with trypsin alone, and with an enzyme combination containing pepsin, trypsin and chymotrypsin. Whey protein digests gave a 50 % inhibition (IC50) of ACE activity at concentration ranges within 345–1733 μg/ml. The IC50 values for the 1–30 kDa fractions ranged from 485 to 1134 μg/ml and for the <1 kDa fraction from 109 to 837 mg/ml. Several ACE-inhibitory peptides were isolated from the hydrolysates by reversed-phase chromatography, and the potencies of the purified peptide fractions had IC50 values of 77–1062 μM. The ACE-inhibitory peptides identified were α-lactalbumin fractions (50–52), (99–108) and (104–108) and β-lactoglobulin fractions (22–25), (32–40), (81–83), (94–100), (106–111) and (142–146).

We have examined potential mechanisms by which the Pim-1 kinase acts as a hematopoietic cell survival factor. Enforced expression of the wild type 33 kd (FD/hpim33) and 44 kd (FD/mpim44) Pim-1 proteins in murine factor-dependent FDCP1 cells prolonged survival after withdrawal of IL-3, while expression of a dominant negative Pim-1 protein (FD/pimNT81) shortened survival. Following removal of IL-3 FDCP1 cells exhibited loss of mitochondrial transmembrane potential and production of reactive oxygen species, as determined bȳ ow cytometry analysis. The wild type Pim-1 proteins decreased these changes while the dominant negative protein enhanced mitochondrial dysfunction. The antiapoptotic activity of the kinases could not be attributed to modulation of glutathione, catalase, or superoxide dismutase activities. Both the FD/hpim33 and FD/ mpim44 cells maintained expression of bcl-2 mRNA following cytokine removal, while a substantial decrease was seen in FD/neo cells. To modulate Bcl-2 protein levels, a bcl-2 antisense RNA construct was coexpressed with the wild type pim-1 cDNAs. FD/hpim33 cells with low cellular Bcl-2 protein levels had shortened cytokineindependent survival compared with FD/hpim33 clones with high Bcl-2 expression. However survival of FD/ mpim44 cells after IL-3 withdrawal was substantially independent of cellular Bcl-2 protein levels. The 33 kd protein delayed, and the 44 kd protein completely prevented enhanced cell death associated with enforced expression of human Bax protein however. Our results suggest that the 33 kd Pim-1 kinase may enhance cell survival through cooperation with and regulation of bcl-2. In addition the 44 kd kinase may regulate the expression or activity of other pro-and anti-apoptotic members of the bcl-2 family.

Pim-1 is an oncogenic serine/threonine kinase implicated in cytokine-induced signal transduction and in development of lymphoid malignancies. However, its precise function as well as physiological substrates have remained unknown. In this study we demonstrate that Pim-1 can physically interact with the NFATc1 transcription factor and phosphorylate it in vitro on several serine residues. In contrast to previously recognized NFATc kinases, wild-type Pim-1 enhances NFATc-dependent transactivation and IL-2 production in Jurkat T cells, while kinase-deficient Pim-1 mutants inhibit them in a dominant negative fashion. Our results reveal a novel, phosphorylation-dependent regulatory mechanism targeting NFATc1 through which Pim-1 acts as a downstream effector of Ras to facilitate IL-2-dependent proliferation and/or survival of lymphoid cells.

We have cloned a novel quail cDNA with strong homology to the pim family of proto-oncogenes. The deduced amino acid (aa) sequence of the cDNA, named qpim, is more closely related to Xenopus Pim and to the recently identi®ed rat Pim-3 than to human or rodent Pim-1 or Pim-2. The protein encoded by the qpim cDNA can autophosphorylate itself and share substrates with murine Pim-1, suggesting functional redundancy to other Pim family serine/threonine kinases. We have compared the expression of qpim in avian embryos to mouse pim-1, -2 and -3 by in situ hybridization. qpim shows a highly dynamic expression pattern, particularly at early developmental stages. Surprisingly, its expression pattern is not identical to any of the murine pim genes, which show complementary and/or partially overlapping expression sites both in-and outside of the hematopoietic system. Altogether, our results suggest novel functions for Pim family kinases during embryonic development, in particular in epithelia and in the central nervous system.