抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Mitogen-activated protein (MAP) kinases comprise a family of ubiquitous proline-directed, protein-serine/threonine kinases, which participate in signal transduction pathways that control intracellular events including acute responses to hormones and major developmental changes in organisms. MAP kinases lie in protein kinase cascades. This review discusses the regulation and functions of mammalian MAP kinases. Nonenzymatic mechanisms that impact MAP kinase functions and findings from gene disruption studies are highlighted. Particular emphasis is on ERK1/2.

/pdf/mitogen-activated-protein-map-kinase-pathways-regulation-and-3nsauvepr2.pdf

Mitogen-activated protein (MAP) kinase pathways: regulation and physiological functions.

The specificities of 65 compounds reported to be relatively specific inhibitors of protein kinases have been profiled against a panel of 70-80 protein kinases. On the basis of this information, the effects of compounds that we have studied in cells and other data in the literature, we recommend the use of the following small-molecule inhibitors: SB 203580/SB202190 and BIRB 0796 to be used in parallel to assess the physiological roles of p38 MAPK (mitogen-activated protein kinase) isoforms, PI-103 and wortmannin to be used in parallel to inhibit phosphatidylinositol (phosphoinositide) 3-kinases, PP1 or PP2 to be used in parallel with Src-I1 (Src inhibitor-1) to inhibit Src family members; PD 184352 or PD 0325901 to inhibit MKK1 (MAPK kinase-1) or MKK1 plus MKK5, Akt-I-1/2 to inhibit the activation of PKB (protein kinase B/Akt), rapamycin to inhibit TORC1 [mTOR (mammalian target of rapamycin)-raptor (regulatory associated protein of mTOR) complex], CT 99021 to inhibit GSK3 (glycogen synthase kinase 3), BI-D1870 and SL0101 or FMK (fluoromethylketone) to be used in parallel to inhibit RSK (ribosomal S6 kinase), D4476 to inhibit CK1 (casein kinase 1), VX680 to inhibit Aurora kinases, and roscovitine as a pan-CDK (cyclin-dependent kinase) inhibitor. We have also identified harmine as a potent and specific inhibitor of DYRK1A (dual-specificity tyrosine-phosphorylated and -regulated kinase 1A) in vitro. The results have further emphasized the need for considerable caution in using small-molecule inhibitors of protein kinases to assess the physiological roles of these enzymes. Despite being used widely, many of the compounds that we analysed were too non-specific for useful conclusions to be made, other than to exclude the involvement of particular protein kinases in cellular processes.

https://hal.archives-ouvertes.fr/hal-00478827/document

The selectivity of protein kinase inhibitors: a further update.

Conserved signaling pathways that activate the mitogen-activated protein kinases (MAPKs) are involved in relaying extracellular stimulations to intracellular responses. The MAPKs coordinately regulate cell proliferation, differentiation, motility, and survival, which are functions also known to be mediated by members of a growing family of MAPK-activated protein kinases (MKs; formerly known as MAPKAP kinases). The MKs are related serine/threonine kinases that respond to mitogenic and stress stimuli through proline-directed phosphorylation and activation of the kinase domain by extracellular signal-regulated kinases 1 and 2 and p38 MAPKs. There are currently 11 vertebrate MKs in five subfamilies based on primary sequence homology: the ribosomal S6 kinases, the mitogen- and stress-activated kinases, the MAPK-interacting kinases, MAPK-activated protein kinases 2 and 3, and MK5. In the last 5 years, several MK substrates have been identified, which has helped tremendously to identify the biological role of the members of this family. Together with data from the study of MK-knockout mice, the identities of the MK substrates indicate that they play important roles in diverse biological processes, including mRNA translation, cell proliferation and survival, and the nuclear genomic response to mitogens and cellular stresses. In this article, we review the existing data on the MKs and discuss their physiological functions based on recent discoveries.

/pdf/erk-and-p38-mapk-activated-protein-kinases-a-family-of-xi88207cal.pdf

Erk and p38 mapk-activated protein kinases: a family of protein kinases with diverse biological functions

SUMMARY The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

Activation and Function of the MAPKs and Their Substrates, the MAPK-Activated Protein Kinases

http://www.oncoveterinaria.com.ar/contenidos/archivos/file/Julio/estrogen%20phosphorylation.pdf

Estrogen receptor phosphorylation

The estrogen receptor α (ER) belongs to a superfamily of ligand-activated transcription factors whose transcriptional activities are influenced by various second messenger signaling pathways. In common with other steroid hormone receptors, the ER has an N-terminal domain with a hormone-independent transcriptional activation function (AF-1), a central DNA-binding domain, and a C-terminal ligand-binding domain with a hormone-dependent transcriptional activation function (AF-2) (18).

Like other members of the steroid receptor superfamily, the ER becomes hyperphosphorylated in the presence of its ligand and several nonsteroidal agents including epidermal growth factor (EGF) (32). Transcriptional activation by EGF has been shown to require AF-1 but not AF-2 (5, 15). EGF stimulates the mitogen-activated protein kinase (MAPK) pathway and causes an increase in the level of phosphorylation of Ser-118 in the human ER (5, 15). Ser-118 appears to be a critical residue in EGF-dependent transcriptional activation of the ER, because mutation of Ser-118 to Ala causes a reduction in the level of transcription (5). However, EGF has a role in addition to phosphorylating Ser-118, since EGF could still stimulate transcription from a mutant ER in which Ser-118 was replaced by Glu (5).

EGF also leads to the activation of the 90-kDa ribosomal S6 kinase (pp90rsk1), a Ser/Thr protein kinase. In response to growth factors, pp90rsk1 is phosphorylated by MAPK and is transported into the nucleus (4), where it forms a stable complex with CBP, a transcriptional coactivator (20). The pp90rsk1-CBP complex has been shown to regulate transcription (20). CBP has also been found to associate in a complex that contains the ER (26). Ectopic expression of CBP enhances ER transcriptional activity (26).

Three mammalian isoforms of pp90rsk1 have been previously identified (19). Each of the isoforms contains two nonidentical kinase domains (10). The amino-terminal kinase domain is responsible for phosphorylating exogenous substrates (3, 10). pp90rsk1 has been shown in vitro to phosphorylate Nur 77 (an orphan nuclear receptor), c-Fos, serum response factor (4), and glycogen synthase kinase-3 (9) and in vivo to phosphorylate IκBα (25).

There is evidence to suggest that in the human ER, Ser-167, like Ser-118, becomes significantly phosphorylated in response to estradiol (1). Ser-167 is contained within the sequence RLASTND. In vitro evidence suggests that casein kinase II phosphorylates Ser-167 (1) and that this residue may be important in DNA binding (1, 29). However, the sequence RXXS is identical to the site in c-Fos which is phosphorylated by pp90rsk1 (6). Therefore, based on the sequence match to a known pp90rsk1 phosphorylation site and the fact that both pp90rsk1 and the ER are known to interact with CBP, we investigated the possibility that pp90rsk1 plays a role in ER-mediated transcription.

Taken together, our results strongly suggest that pp90rsk1 phosphorylates Ser-167 of the human ER in vivo and that Ser-167 aids in regulating the transcriptional activity of AF-1 in the ER. These results suggest that phosphorylation of the ER by pp90rsk1 is involved in ER-mediated transcription.

pp90rsk1 regulates estrogen receptor-mediated transcription through phosphorylation of Ser-167.

p90 ribosomal S6 kinase (RSK) is an important downstream effector of mitogen-activated protein kinase, but its biological functions are not well understood. We have now identified the first small-molecule, RSK-specific inhibitor, which we isolated from the tropical plant Forsteronia refracta . We have named this novel inhibitor SL0101. SL0101 shows remarkable specificity for RSK. The major determinant of SL0101-binding specificity is the unique ATP-interacting sequence in the amino-terminal kinase domain of RSK. SL0101 inhibits proliferation of the human breast cancer cell line MCF-7, producing a cell cycle block in G 1 phase with an efficacy paralleling its ability to inhibit RSK in intact cells. RNA interference of RSK expression confirmed that RSK regulates MCF-7 proliferation. Interestingly, SL0101 does not alter proliferation of a normal human breast cell line MCF-10A, although SL0101 inhibits RSK in these cells. We show that RSK is overexpressed in ∼50% of human breast cancer tissue samples, suggesting that regulation of RSK has been compromised. Thus, we show that RSK has an unexpected role in proliferation of transformed cells and may be a useful new target for chemotherapeutic agents. SL0101 will provide a powerful new tool to dissect the molecular functions of RSK in cancer cells.

/pdf/identification-of-the-first-specific-inhibitor-of-p90-2b31wr4q0c.pdf

Identification of the First Specific Inhibitor of p90 Ribosomal S6 Kinase (RSK) Reveals an Unexpected Role for RSK in Cancer Cell Proliferation

Estradiol-induced Phosphorylation of Serine 118 in the Estrogen Receptor Is Independent of p42/p44 Mitogen-activated Protein Kinase

An increase in the activity of mitogen-activated protein kinase (MAPK) has been correlated with the progression of prostate cancer to advanced disease in humans. The serine/threonine protein kinase p90-kDa ribosomal S6 kinase (RSK) is an important downstream effector of MAPK but its role in prostate cancer has not previously been examined. Increasing RSK isoform 2 (RSK2) levels in the human prostate cancer line, LNCaP, enhanced prostate-specific antigen (PSA) expression, an important diagnostic marker for prostate cancer, whereas inhibiting RSK activity using a RSK-specific inhibitor, 3Ac-SL0101, decreased PSA expression. The RSK2 regulation of PSA expression occurred via a mechanism involving both RSK2 kinase activity and its ability to associate with the coactivator, p300. RNA interference of the androgen receptor (AR) showed that the AR was important in the RSK2-mediated increase in PSA expression. RSK levels are higher in approximately 50% of human prostate cancers compared with normal prostate tissue, which suggests that increased RSK levels may participate in the rise in PSA expression that occurs in prostate cancer. Furthermore, 3Ac-SL0101 inhibited proliferation of the LNCaP line and the androgen-independent human prostate cancer line, PC-3. These results suggest that proliferation of some prostate cancer cells is dependent on RSK activity and support the hypothesis that RSK may be an important chemotherapeutic target for prostate cancer.

https://cancerres.aacrjournals.org/content/canres/65/8/3108.full.pdf

Deborah A. Lannigan

Papers

Estrogen receptor phosphorylation

pp90rsk1 regulates estrogen receptor-mediated transcription through phosphorylation of Ser-167.

Identification of the First Specific Inhibitor of p90 Ribosomal S6 Kinase (RSK) Reveals an Unexpected Role for RSK in Cancer Cell Proliferation

Estradiol-induced Phosphorylation of Serine 118 in the Estrogen Receptor Is Independent of p42/p44 Mitogen-activated Protein Kinase

The Serine/Threonine Protein Kinase, p90 Ribosomal S6 Kinase, Is an Important Regulator of Prostate Cancer Cell Proliferation