Abstract 1455: The glucocorticoid receptor-LEDGFp75 interaction in prostate cancer therapy cross-resistance

Prostate cancer (PCa) is the second leading cause of cancer deaths in the U.S., disproportionally affecting African American (AA) men. PCa patients with recurrent disease develop therapy resistance and fail to respond to both anti-androgen receptor signaling (ARSI) therapy and taxane-based chemotherapy. Glucocorticoid receptor, a transcription factor, has been implicated in resistance to ARSI (via the GR bypass), and docetaxel (DTX) therapies. However, the mechanisms underlying this GR-mediated therapy cross-resistance are poorly understood. Previously, we demonstrated that glucocorticoids, which are co-administered with current PCa therapies and activate GR signaling, upregulate the chemoresistance-associated transcription coactivator LEDGFp75 in PCa cells. We also identified consensus GR binding sites in the promoter region of the gene encoding LEDGFp75, suggesting it is a GR target gene. We hypothesized that GR transcriptionally upregulates LEDGFp75 and then interacts with this protein in the nucleus to promote DTX resistance in PCa cells. Genetic silencing of GR in a panel of DTX-sensitive and -resistant PCa cell lines decreased the expression of LEDGFp75 at both the protein and transcript levels, confirming its status as a candidate GR target gene. However, genetic silencing of LEDGFp75 had no effects on GR protein expression. Pharmacological inhibition of GR also decreased LEDGFp75 in DTX-sensitive cells. The effects of Exicorilant and Relacorilant (Corcept Therapeutics) were evaluated on LEDGFp75 protein expression levels. Immunoprecipitation and confocal microscopy studies revealed that GR and LEDGFp75 interact in the nucleus of PCa cells. Interestingly, upregulation of GR in enzalutamide resistant LNCaP cells correlated with LEDGFp75 upregulation, and GR silencing in these cells decreased this upregulation. These results suggested a possible role for GR and LEDGFp75 in PCa therapy cross-resistance. Further studies are underway to determine if co-targeting these two proteins genetically and pharmacologically attenuates both enzalutamide resistance and DTX resistance and other aggressive properties of PCa cells. In addition, RNAseq studies have been initiated to determine the degree of transcriptional overlap between GR and LEDGFp75 in chemoresistant PCa cells. Our goal is to link mechanistically the GR-LEDGFp75 transcriptional network to ARSI/taxane cross-resistance in PCa and target this network to attenuate therapy resistance.

Citation Format: Evelyn S. Sanchez-Hernandez, Pedro T. Ochoa, Greisha L. Ortiz-Hernandez, Shannalee Martinez, Carlos Casiano. The glucocorticoid receptor-LEDGFp75 interaction in prostate cancer therapy cross-resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1455.

Use of Complementary and Alternative Medicine for Prostate Cancer among African Americans, African Immigrants and Caribbean Immigrants

Black men have the highest rate of prostate cancer (PCa) morbidity and mortality in the US, and often receive delayed and/or poorer-quality treatment. This inequity has led many to turn to complementary and alternative medicine/therapies (CAM). However, little is known about the use of these therapies within the Black community. The purpose of this study was to describe types of CAM therapies used, and the reasons behind their use for overall health and PCa treatment and prevention among three groups of Black males, namely African Americans, Caribbean Immigrants and African Immigrants. This study used a mixed-methods design with a quantitative phase (n = 575) followed by a qualitative phase (n = 61) with participants recruited from various parts of the country. Results revealed differences among subgroups in CAM use for overall health and PCa, as well as differences in the types of CAM therapies used and differences in the reasons behind their use. The findings of this study reveal a prevalence of CAM use for overall health and PCa within three different groups of Black men and identifies the specific CAM used. There were significant differences in the types of CAM used by each subgroup for both overall health and PCa. This study also shows that there is value in looking at Black subgroups distinctively, for their rates of CAM use and reasons for use, are distinctly different.

African Immigrant Health: Prostate Cancer Attitudes, Perceptions, and Barriers

Prostate cancer (PCa) is the second leading cause of cancer-related death among Black men who present with higher incidence, mortality, and survival compared to other racial groups. African immigrant men, however, are underrepresented in PCa research and thus this research sought to address that gap. This study applied a social determinants of health framework to understand the knowledge, perceptions, and behavioral tendencies regarding PCa in African immigrants. African immigrant men and women residing in different parts of the country (California, Texas, Colorado, Oklahoma, and Florida) from various faith-based organizations, African community groups, and social groups were recruited to participate in key informant interviews (n = 10) and two focus groups (n = 23). Four themes were identified in this study: (a) PCa knowledge and attitudes-while knowledge is very limited, perceptions about prostate health are very strong; (b) culture and gender identity strongly influence African health beliefs; (c) preservation of manhood; and (d) psychosocial stressors (e.g., financial, racial, immigration, lack of community, and negative perceptions of invasiveness of screening) are factors that play a major role in the overall health of African immigrant men. The results of this qualitative study unveiled perceptions, attitudes, beliefs, and knowledge of PCa among African immigrants that should inform the planning, development, and implementation of preventive programs to promote men's health and PCa awareness.

Abstract B05: Differential autoimmune response to glycolysis and plasminogen antigens from aggressive prostate cancer cells in African American and European American men with prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer-related male deaths in the U.S. This cancer is more aggressive in African American (AA) men, who are twice as likely to die from the disease compared to other racial groups. Despite racial disparities in PCa mortality, immunoproteomic studies profiling sera from thousands of men for the presence of autoantibodies to tumor-associated antigens (TAA) have mostly used sera from European or Asian ancestry. These autoantibodies can serve as both cancer biomarkers and potential tools in anti-tumor immunotherapy. In this study we profiled sera of AA and European American (EA) men with (N=157) and without (N=183) PCa against protein lysates from aggressive PCa cell lines using one and two-dimensional Western blotting. Sera from AA-PCa patients showed stronger immunoreactivity to proteins in PC3 cell lysates compared to EA-PCa sera. Common bands of immunoreactivity were observed around 37, 40, 50, 55, 60, and 70 kD from the sera of multiple patients. Several AA-PCa sera showed common immunoreactivity against a 50 kD protein band (16 out of 24, 67%) which was identified by serological proteomic analysis (SERPA) as alpha-enolase (ENO1), an enzyme that participates in both the glycolysis and plasminogen pathways. ELISA using purified ENO1 was conducted on 360 sera and showed significantly elevated frequency in men with PCa compared to non-PCa controls. Interestingly, SERPA analysis of other strongly immunoreactive spots outside the 50 kD region recognized of the other highly reactive PCa sera revealed additional candidate TAAs involved in the glycolysis and plasminogen pathways. These included key glycolytic enzymes GAPDH, fructose bisphosphate aldolase, phosphoglycerate kinase and lactate dehydrogenase, and other members of the plasminogen system such as GRP78 and annexin A2. Autoantibodies to stress survival proteins HSP60 and STIP1 were also identified in multiple PCa sera. We then probed by immunoblotting representative sera recognizing some of these candidate TAAs against a panel of 12 PCa and non-PCa cell lines. Anti-STIP1 sera showed elevated immunoreactivity predominantly in docetaxel-resistant cell lines. In the anti-ENO1 positive sera, we observed a race-related differential immune response, with anti-ENO1 sera from AA-PCa men showing elevated immunoreactivity mostly in metastatic cell lines, and anti-ENO1 sera from EA-PCa men showing uniform immunoreactivity across the entire panel of prostate cell lines. Interestingly, while several anti-ENO1 positive sera from AA-PCa men had increased immunoreactivity to this protein in the metastatic PCa cell lines LNCaP, MDA-PC2b, PC3 and DU145, they lacked reactivity against ENO1 in the docetaxel-resistant PC3-DR and DU145-DR cells, or purified ENO1 used in the ELISA. Anti-ENO1 EA-PCa sera did not display this differential pattern of immunoreactivity. To better understand these differences in anti-ENO1 reactivity, we interrogated the pattern of ENO1 post-translational modifications (PTMs) from PC3, PC3-DR and purified ENO1. Several different acetylated, methylated, phosphorylated, citrullinated, and glycosylated ENO1 PTMs were identified in the PC3 cells that were not present in the PC3-DR cells nor purified ENO1 which might explain the differential reactivity of AA-PCa sera against these three sources of ENO1. Taken together, these data suggest the anti-ENO1 autoantibodies from AA-PCa men may target a modified form of ENO1 that is different from that recognized by EA-PCa men. These discrepancies point to racial differences in immune response to TAAs in prostate tumors, and may have implications for identifying immunobiological factors contributing to PCa health disparities.

Citation Format: Tino W. Sanchez, Guangyu Zhang, Jitian Li, Liping Dai, Rowaid Kellow, Saied Mirshahidi, Nathan R. Wall, Clayton Yates, Colwick Wilson, Susanne Montgomery, Jian-Ying Zhang, Carlos Casiano. Differential autoimmune response to glycolysis and plasminogen antigens from aggressive prostate cancer cells in African American and European American men with prostate cancer. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B05.

Abstract B05: Immunoproteomic profiling in African American men with prostate cancer: Evidence for an autoimmune response to glycolytic enzymes

Prostate cancer (PCa) is the most frequently diagnosed cancer and the second leading cause of cancer-related male deaths in the U.S. This cancer is more aggressive in African American (AA) men, who are twice as likely to die from the disease when compared to other racial groups. Despite these racial disparities in PCa mortality, studies on PCa biology and biomarker discovery include mostly patients from European American (EA) backgrounds. There is a critical need to find minimally invasive PCa biomarkers that could aid in diagnosis and prognosis, especially in high risk populations like AA men. Immunoseroproteomics offers a minimally invasive approach to detect early malignant processes that trigger production of autoantibodies to tumor-associated antigens (TAA). These antibodies serve as “sensors” of tumorigenic events and can be assessed as potential biomarkers relevant to tumor biology. In this study we used this approach to interrogate anti-TAA autoantibody signatures in AA and EA men with PCa and explored racial differences in tumor immunobiology that could underlie PCa mortality disparities. We used serum samples from AA (n=59) and EA (n=50) men with PCa to probe one- and two-dimensional Western blots (WB) of protein lysates from aggressive PCa cell lines. AA PCa patient sera showed stronger immunoreactivity to proteins in PC3 cell lysates compared to the EA sera, with a 50 kD protein band frequently targeted by autoantibodies in several AA PCa sera. Serological proteomic analysis (SERPA) with mass spectrometry showed that these AA PCa autoantibodies recognized alpha-enolase (ENO1), known to be important in tumor formation, expansion, and glucose metabolism. In addition, several other glycolytic enzymes important for tumor proliferation were also identified as candidate prostate TAA, including GAPDH, phosphoglycerate kinase, and lactate dehydrogenase. These have been validated in other studies as overexpressed in PCa. The ENO1 autoantibody frequency, measured by ELISA in sera from 400 racially diverse men with and without PCa, was four-fold higher in PCa compared to non-PCa patients. Interestingly, although sera from AA men with PCa had stronger WB reactivity to ENO1 present in PC3 lysates compared to EA men, and the ENO1 autoantibodies were initially discovered in eight AA PCa sera but only in two EA sera, the anti-ENO1 autoantibody frequency measured by ELISA, which used E. coli-purified recombinant human ENO1 as a substrate, was higher in the EA PCa cohort. In addition, several anti-ENO1 positive sera from AA men with PCa showed increased immunoreactivity to this protein in the PCa cell lines LNCaP, MDA-PC2b, PC3, and DU145, but not against the purified ENO1 used in ELISA. The opposite was true in the EA PCa cohort, where strong reactivity against the purified ENO1 did not correlate with an equally strong immunoreactivity against the cellular ENO1. The EA PCa sera did not recognize the pattern of ENO1 expression observed with the AA sera in the same panel of prostate cell lines. These differences of immunoreactivity between AA and EA sera against PC3-ENO1 vs bacterially purified human ENO1 suggest that select AA sera may predominantly recognize ENO1 epitopes not displayed in the purified protein. A recent study found higher frequency of autoantibodies to phosphorylated ENO1 in pancreatic cancer sera compared to normal patient sera. Our own proteomic comparison of PC3-ENO1 and recombinant ENO1 yielded differences in phosphorylated, acetylated, and methylated amino acids. Taken together, these data suggest the anti-ENO1 autoantibodies from AA men with PCa target a modified form of ENO1 that may not be strongly recognized by EA men with PCa. These discrepancies point to racial differences in the immune response to prostate tumors.

Citation Format: Tino Wilson Sanchez, Jitian Li, Liping Dai, Saied Mirshahidi, Guangyu Zhang, Nathan Wall, Colwick Wilson, Susanne Montgomery, Jianying Zhang, Carlos Casiano. Immunoproteomic profiling in African American men with prostate cancer: Evidence for an autoimmune response to glycolytic enzymes. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr B05.

Abstract 5411: Repositioning HIV-based small molecule inhibitors of the stress survival oncoprotein LEDGF/p75 to overcome taxane resistance in prostate cancer

Prostate cancer (PCa) is the second most commonly diagnosed cancer in men and the leading cause of cancer-related deaths in elderly males. Although early stage PCa is treatable, many patients eventually develop castration-resistant disease (mCRPC), characterized by metastasis and resistance to therapy. Furthermore, PCa also presents a major health disparity problem as evidenced by its disproportionately high incidence and mortality in African American men compared to other racial/ethnic groups. Reducing or eliminating these disparities in PCa mortality will require innovative therapeutic approaches to circumvent chemoresistance and increase patient survival. We have previously demonstrated that lens epithelium-derived growth factor of 75 kD (LEDGF/p75) is a stress survival protein that is overexpressed in PCa cells and clinical tumors, and promotes resistance to Docetaxel (DTX), the gold standard for mCRPC chemotherapy. LEDGF/p75 has also been extensively studied as a target to inhibit HIV-1 integration into host chromatin because of its role as a key cellular cofactor of HIV integrase (IN). A series of novel and potent small molecule inhibitors (SMI) of LEDGF/p75 were previously evaluated for their potential to disrupt its interaction with HIV-IN. We hypothesized that repositioning these SMI to target LEDGF/p75 in the context of PCa could be a promising strategy for overcoming taxane resistance. We observed that PC3 and DU145 mCRPC cells selected for DTX resistance expressed high levels of LEDGF/p75, and were also resistant to the taxanes Cabazitaxel (CTX) and Paclitaxel (PTX). This chemoresistance was selective since LEDGF/p75 did not protect cells against the classical apoptotic inducer TRAIL, which triggers caspase-mediated cleavage and inactivation of LEDGF/p75. RNAi-mediated knockdown of LEDGF/p75 in these cell lines sensitized them to taxane therapy. We then evaluated 130 LEDGF/p75 SMI for their cytotoxicity in DTX-resistant and sensitive PC3 and DU145 cells, in the presence and absence of DTX. These experiments yielded a number of inhibitors that induced cell death directly or re-sensitized resistant cells to taxanes only when combined with these drugs. Our results suggest that LEDGF/p75 is a druggable oncoprotein that could be targeted with repositioned HIV-based SMI to overcome PCa chemoresistance.

Citation Format: Leslimar Rios Colon, Catherine Elix, Ivana Alicea, Anamika Basu, Christina Du Ross, Tino Sanchez, Nouri Neamati, Carlos Casiano. Repositioning HIV-based small molecule inhibitors of the stress survival oncoprotein LEDGF/p75 to overcome taxane resistance in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5411. doi:10.1158/1538-7445.AM2015-5411

Abstract 3117: Overexpression of the stress transcription co-activator LEDGF/p75 contributes to the upregulation of the stress protective genes HSP27, ERp57 and CYGB in prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed cancer and the second leading cause of cancer related death in men in the US. PCa tumor aggressiveness, response to treatment, and mortality are worst in African-American men, compared to other ethnic groups, thus presenting a major health disparity. Our group reported previously that lens epithelium derived growth factor p75 (LEDGF/p75), a stress survival transcription coactivator, has elevated expression in PCa cells and tissues and promotes resistance to cell death induced by oxidative stress and chemotherapy. This is likely due to its ability to transactivate promoter regions of stress and antioxidant genes such as peroxiredoxin 6 (Prdx6) and heat shock protein 27 (HSP27). We hypothesized that high expression of LEDGF/p75 in prostate tumor cells and tissues contributes to the elevated expression of its putative target genes, some of which were identified in previous studies by our group and others. These include genes associated with stress protection and chemotherapy resistance such as HSP27, endoplasmic reticulum protein 57 (ERp57), and cytoglobin (CYGB). To test this hypothesis we performed an expression analysis of LEDGF/p75, HSP27, ERp57 and CYGB proteins in human PCa cell lines using immunoblotting, and in prostate tumor tissues using immunohistochemistry on tumor tissue microarrays (TMAs). PCa cell lines included stable PC3 clones overexpressing LEDGF/p75, as well as docetaxel (DTX) resistant PC3-DR and DU145-DR cells overexpressing this protein, with their corresponding parental DTX sensitive cell lines. The TMAs contained tissue specimens corresponding to prostate tumor, hyperplasia, normal-adjacent, and disease-free normal prostate tissues. Correlations between the expression of LEDGF/p75 and HSP27 or ERp57 or CYGB in cell lines as well as in tumors and normal tissues was determined. Our results indicated that overexpression of LEDGF/p75 in PC3 stable clones and in DTX resistant PCa cells was associated with increased protein expression of HSP27, ERp57 and CYGB. Statistically significant correlation was also observed between the protein levels of LEDGF/p75 and HSPp27 or ERp57 or CYGB in the TMAs. Luciferase-based transcription reporter assays confirmed that the promoter regions of HSP27 and ERp57 are activated by LEDGF/p75 in PCa cells. Chromatin immunoprecipitation assays also demonstrated binding of LEDGF/p75 to HSP27 promoter in PCa cells. Additional promoter activation studies are in progress to demonstrate that LEDGF/p75 transcriptionally regulates ERp57 and CYGB genes. These results enhance our understanding of the contribution of LEDGF/p75 overexpression to the activation of stress protective genes and its implications for chemotherapy resistance in metastatic PCa.

Citation Format: Anamika Basu, Christina Cajigas, Benanette Medina, Heather Rojas, Hiya Banerjee, Melanie Mediavilla-Varela, Laisum Leoh, Carlos Casiano. Overexpression of the stress transcription co-activator LEDGF/p75 contributes to the upregulation of the stress protective genes HSP27, ERp57 and CYGB in prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3117. doi:10.1158/1538-7445.AM2013-3117

Abstract 775: Targeting the transcriptional coactivator LEDGF/p75 to overcome chemoresistance in prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer death among men in the US, with African American men presenting a disproportionately high incidence and mortality. Reducing this mortality disparity requires developing novel strategies for overcoming prostate tumor chemoresistance. Currently, chemotherapy with Docetaxel (DTX), the standard of care for advanced PCa, is limited because most patients treated with the drug ultimately develop chemoresistance and succumb to the disease. Circumventing this resistance is therefore essential for increasing the effectiveness of DTX and other anti-PCa drugs. Our group has established previously that lens ephitelium-derived growth factor p75 (LEDGF/p75), a stress survival oncoprotein, is overexpressed in human prostate tumors, and that its overexpression in PCa cell models promotes resistance to DTX via inhibition of lysosomal cell death. The present study was designed to evaluate if overexpression of LEDGF/p75 in PCa cells also promotes resistance to other chemotheurapeutic drugs, and if its depletion sensitizes chemoresistant PCa cells to drug-induced cell death. First, we treated PC-3 cells (with and without stable LEDGF/p75 overexpression) with increasing concentrations of DTX, paclitaxel, doxorubicin, and TRAIL for up to 48 hrs. We then assessed cell viability by MTT assays and morphological examination. LEDGF/p75 overexpressing PC-3 cells showed higher viability than parental PC-3 cells in response to DTX, paclitaxel, and doxorubicin. However, LEDGF/p75 did not protect against TRAIL-induced cell death, indicating selectivity in the ability of this stress oncoprotein to induce chemoresistance. We also observed by immunoblotting and quantitative PCR that metastatic PCa cell lines selected for DTX resistance, designated PC3-DR and DU-145DR, naturally express high levels of endogenous LEDGF/p75 relative to their sensitive parental cell lines. To assess the contribution of elevated LEDGF/p75 expression to DTX resistance in these two cell lines, we knocked down this protein with a specific small inhibitory RNA (si-p75). Immunoblots showed that si-p75 depleted cells of LEDGF/p75. Cell viability significantly decreased in both PC3-DR and DU-145DR cell lines in response to combined treatment with DTX and si-p75, relative to scrambled siRNA control. Our preliminary results suggest that LEDGF/p75 overexpression promotes chemoresistance in cellular models of advanced PCa, and that its inhibition increases sensitization to DTX. These promising results have implications for the development of novel theraupetic strategies for chemoresistant PCa. Further studies are in progress to determine the spectrum of anti-PCa drugs antagonized by LEDGF/p75, and if depletion of this protein sensitizes PCa cells to a wide variety of antitumor drugs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 775. doi:1538-7445.AM2012-775

Protein topography of Sulfolobus solfataricus ribosomes by cross-linking with 2-iminothiolane. Sso L12e, Sso L10e, and Sso L11e are neighbors

Large ribosomal subunits from Sulfolobus solfataricus were cross-linked with 2-iminothiolane in order to investigate the arrangement of proteins in the region containing the multicopy acidic protein Sso L12e, the protein homologous to Escherichia coli L7/L12. Proteins from cross-linked 50 S subunits were extracted and fractionated by chromatography on CM-cellulose. Fractions containing Sso L12e were analyzed by "diagonal" (two-dimensional reducing/nonreducing) dodecyl sulfate polyacrylamide gel electrophoresis. Sso L12e appeared in cross-linked homodimers and also in cross-linked complexes that contained Sso L10e, the protein equivalent to E. coli L10. In addition, Sso L12e was found in cross-links to L4, L6a, L26, and L29. N-terminal sequences obtained for L6a and L26 showed them to have significant homologies to E. coli proteins L11 and L23, respectively. The results indicate the presence in this archaebacterial ribosome of Sso L12e dimers and their location near Sso L10e and Sso L11e. The Sso L12e-L29 (Sso L23e) cross-link suggests proximity between components of the factor-binding and peptidyltransferase domains, since E. coli L23 is a protein affinity-labeled by puromycin. The (Sso L12e)4-Sso L10 pentameric complex, identified previously from studies in solution, appears to represent correctly the arrangement of these proteins in the ribosome. The occurrence in the archaebacterial ribosome of this unique structural element, similar to those shown previously in eubacteria and eukaryotes, reinforces the concept that the protein quaternary structure of the ribosomal factor-binding domain is highly conserved.

Occurrence in the archaebacterium Sulfolobus solfataricus of a ribosomal protein complex corresponding to Escherichia coli (L7/L12)4.L10 and eukaryotic (P1)2/(P2)2.P0

Two-dimensional electrophoresis of total protein from 50 S ribosomal subunits of the archaebacterium Sulfolobus solfataricus demonstrated a complex between two proteins that was stable in 6 M urea, but dissociable in detergent or below pH 5.5. The proteins, numbered L1 and L10 according to their electrophoretic mobilities, corresponded to Escherichia coli ribosomal proteins L10 and L7/L12, respectively. The members of the complex were therefore designated Sso L10e and Sso L12e. Sso L12e had other properties in common with E. coli L7/L12: low molecular weight, relative acidity, selective release from the ribosome by high salt/ethanol, and dimeric structure. The Sso L12e.Sso L10e complex was isolated by gel filtration of total 50 S proteins in 4 M urea. The stoichiometry of the components was approximately four copies of Sso L12e to one copy of Sso L10e. The occurrence in an archaebacterium of a complex of acidic ribosomal proteins similar to E. coli (L7/L12)4.L10 and eukaryotic (P1)2/(P2)/.P0 strongly supports the concept that this element of quaternary structure is a major conserved feature of the ribosome and reaffirms its importance in the translocation step of protein synthesis.

Preparation and characterization of two monoclonal antibodies against different epitopes in Escherichia coli ribosomal protein L7/L12

Two monoclonal antibodies with specificities for Escherichia coli 50 S ribosomal subunit protein L7/L12 were isolated. The antibodies and Fab fragments thereof were purified by affinity chromatography using solid-phase coupled L7/L12 protein as the immunoadsorbent. The two antibodies were shown to recognize different epitopes; one in the N-terminal and the other in the C-terminal domain of protein L7/L12. Both intact antibodies strongly inhibited polyuridylic acid-directed polyphenylalanine synthesis, ribosome-dependent GTPase activity, and the binding of elongation factor EF-G to the ribosome. Ratios of antibody to ribosome of 4:1 or less were effective in inhibiting these activities. Neither antibody prevented the association of ribosomal subunits to form 70 S ribosomes. The Fab fragments showed similar effects.