Efficacy of National Comprehensive Cancer Network Guidelines in Identifying Pathogenic Germline Variants Among Unselected Patients with Prostate Cancer: The PROCLAIM Trial

BACKGROUND

Prostate cancer (PCa) patients with pathogenic/likely pathogenic germline variants (PGVs) in cancer predisposition genes may be eligible for U.S. Food and Drug Administration-approved targeted therapies, clinical trials, or enhanced screening. Studies suggest that eligible patients are missing genetics-informed care due to restrictive testing criteria.

OBJECTIVE

To establish the prevalence of actionable PGVs among prospectively accrued, unselected PCa patients, stratified by their guideline eligibility.

DESIGN, SETTING, AND PARTICIPANTS

Consecutive, unselected PCa patients were enrolled at 15 sites in the USA from October 2019 to August 2021, and had multigene cancer panel testing.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Correlates between the prevalence of PGVs and clinician-reported demographic and clinical characteristics were examined.

RESULTS AND LIMITATIONS

Among 958 patients (median [quartiles] age at diagnosis 65 [60, 71] yr), 627 (65%) had low- or intermediate-risk disease (grade group 1, 2, or 3). A total of 77 PGVs in 17 genes were identified in 74 patients (7.7%, 95% confidence interval [CI] 6.2-9.6%). No significant difference was found in the prevalence of PGVs among patients who met the 2019 National Comprehensive Cancer Network Prostate criteria (8.8%, 43/486, 95% CI 6.6-12%) versus those who did not (6.6%, 31/472, 95% CI 4.6-9.2%; odds ratio 1.38, 95% CI 0.85-2.23), indicating that these criteria would miss 42% of patients (31/74, 95% CI 31-53%) with PGVs. The criteria were less effective at predicting PGVs in patients from under-represented populations. Most PGVs (81%, 60/74) were potentially clinically actionable. Limitations include the inability to stratify analyses based on individual ethnicity due to low numbers of non-White patients with PGVs.

CONCLUSIONS

Our results indicate that almost half of PCa patients with PGVs are missed by current testing guidelines. Comprehensive germline genetic testing should be offered to all patients with PCa.

PATIENT SUMMARY

One in 13 patients with prostate cancer carries an inherited variant that may be actionable for the patient's current care or prevention of future cancer, and could benefit from expanded testing criteria.

Democratizing germline genetic testing and its impact on prostate cancer clinical decision-making

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Background: Approximately 10-15% of prostate cancer (PCa) patients (pts) have a pathogenic germline variant (PGV). Identification of a PGV has important implications affecting decisions regarding cancer screening, treatment selection, and family cascade testing. There exists limited data documenting real world recommendations post germline genetic testing (GGT). This study was designed to collect clinician reported outcomes from PCa pts who underwent GGT. Methods: An IRB-approved, nationwide, prospective registry recruited unselected PCa pts from 15 community and academic urology practices. Pts underwent an 84-gene panel test, with clinical outcomes collected via clinician-completed case report forms > 1-month post GGT. Statistical significance was determined by two-tailed Fisher’s exact test. Results: 982 predominantly white (75.9%), non-metastatic (80.7%) males with PCa were recruited; 56.9% met National Comprehensive Cancer Network (NCCN) GGT criteria. Average age was 65.3 years at PCa diagnosis. PGVs, most commonly CHEK2 (17) and BRCA2 (10), were identified in 100 (10.2%) pts; 34 (34%) of these did not meet NCCN GGT criteria. Among PGV positive pts, 241 recommendations were made (Table). They were more likely to have changes to treatment (p < 0.0001), follow up (p < 0.0001) and cascade testing recommendations (p < 0.0001) than those with negative/variant of uncertain significance (VUS) results. There were no significant differences in changes to treatment (p = 0.4471) or follow up (p = 0.861) for pts who met NCCN criteria versus those who did not. 7 pts with PGVs received targeted therapy or were referred to a clinical trial. 5 pts with VUS results were also referred to a clinical trial. Among these 12 pts, 6 (50%, 2 CHEK2 PGV, 1 ATM PGV, 1 VUS each ATM, BLM, CHEK2) did not meet NCCN GGT criteria. Referral to a genetic counselor was the most common follow up recommendation for those with PGV (38 patients, 38%) and VUS results (66, 13.7%). The most commonly reported impact to health outcomes for those with negative results was knowledge/reassurance (38, 7.88%). Conclusions: This study showed that GGT did influence PCa pts care. Appropriately, pts with PGVs received a greater number of recommendations for relatives, changes to follow up and treatment. [Table: see text]

Motility phenotype in a zebrafish vmat2 mutant

In the present study, we characterize a novel zebrafish mutant of solute carrier 18A2 (slc18a2), also known as vesicular monoamine transporter 2 (vmat2), that exhibits a behavioural phenotype partially consistent with human Parkinson´s disease. At six days-post-fertilization, behaviour was analysed and demonstrated that vmat2 homozygous mutant larvae, relative to wild types, show changes in motility in a photomotor assay, altered sleep parameters, and reduced dopamine cell number. Following an abrupt lights-off stimulus mutant larvae initiate larger movements but subsequently inhibit them to a lesser extent in comparison to wild-type larvae. Conversely, during a lights-on period, the mutant larvae are hypomotile. Thigmotaxis, a preference to avoid the centre of a behavioural arena, was increased in homozygotes over heterozygotes and wild types, as was daytime sleep ratio. Furthermore, incubating mutant larvae in pramipexole or L-Dopa partially rescued the motor phenotypes, as did injecting glial cell-derived neurotrophic factor (GDNF) into their brains. This novel vmat2 model represents a tool for high throughput pharmaceutical screens for novel therapeutics, in particular those that increase monoamine transport, and for studies of the function of monoamine transporters.

Exome sequencing provides additional evidence for the involvement of ARHGAP29 in Mendelian orofacial clefting and extends the phenotypic spectrum to isolated cleft palate

BACKGROUND

Recent advances in genomics methodologies, in particular the availability of next-generation sequencing approaches have made it possible to identify risk loci throughout the genome, in particular the exome. In the current study, we present findings from an exome study conducted in five affected individuals of a multiplex family with cleft palate only.

METHODS

The GEnome MINIng (GEMINI) pipeline was used to functionally annotate the single nucleotide polymorphisms, insertions and deletions. Filtering methods were applied to identify variants that are clinically relevant and present in affected individuals at minor allele frequencies (≤1%) in the 1000 Genomes Project single nucleotide polymorphism database, Exome Aggregation Consortium, and Exome Variant Server databases. The bioinformatics tool Systems Tool for Craniofacial Expression-Based Gene Discovery was used to prioritize cleft candidates in our list of variants, and Sanger sequencing was used to validate the presence of identified variants in affected and unaffected relatives.

RESULTS

Our analyses approach narrowed the candidates down to the novel missense variant in ARHGAP29 (GenBank: NM_004815.3, NP_004806.3;c.1654T>C [p.Ser552Pro]. A functional assay in zebrafish embryos showed that the encoded protein lacks the activity possessed by its wild-type counterpart, and migration assays revealed that keratinocytes transfected with wild-type ARHGAP29 migrated faster than counterparts transfected with the p.Ser552Pro ARHGAP29 variant or empty vector (control).

CONCLUSION

These findings reveal ARHGAP29 to be a regulatory protein essential for proper development of the face, identifies an amino acid that is key for this, and provides a potential new diagnostic tool.Birth Defects Research 109:27-37, 2017. © 2016 Wiley Periodicals, Inc.

SLC41A1 and TRPM7 in magnesium homeostasis and genetic risk for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder of the central nervous system with a clinically heterogeneous presentation that includes progressive loss of dopaminergic (DA) neurons in the substantia nigra. A minority of PD cases are familial and are caused by mutations in single genes. Most cases, however, are idiopathic PD, a complex multifactorial disorder with environmental and genetic contributors to etiology. Here, we first briefly summarize published evidence that among environmental contributors is dietary deficiency of magnesium. We then review genetic data suggesting that mutations in genes encoding two proteins contributing to cellular magnesium homeostasis confer risk for PD or other Parkinsonian conditions. First, the gene encoding magnesium transporter SLC41A1 is, among others, a candidate for the causative gene in the PARK16 locus where variation is associated with risk for idiopathic Parkinsonian disease. Studies of the function of SLC41A1 in animal models are needed to test whether this protein has a role in maintenance of dopaminergic neurons. Second, in a small study, a hypomorphic variant of TRPM7, a magnesium-permeable channel, was over-represented in cases of amyotrophic lateral sclerosis/ Parkinson dementia complex versus controls from the same ethnic group. Although this association was not detected in a second study, in zebrafish Trpm7 is necessary for terminal differentiation and reduction of toxin-sensitivity in dopaminergic neurons. Overall, epidemiological results support the possibility that mutations in genes relevant to magnesium homeostasis would alter PD risk, but deeper genetic analyses of PD patients are necessary to confirm whether SLC41A1 and TRPM7 are among such genes.

A polymorphism in IRF4 affects human pigmentation through a tyrosinase-dependent MITF/TFAP2A pathway

Sequence polymorphisms linked to human diseases and phenotypes in genome-wide association studies often affect noncoding regions. A SNP within an intron of the gene encoding Interferon Regulatory Factor 4 (IRF4), a transcription factor with no known role in melanocyte biology, is strongly associated with sensitivity of skin to sun exposure, freckles, blue eyes, and brown hair color. Here, we demonstrate that this SNP lies within an enhancer of IRF4 transcription in melanocytes. The allele associated with this pigmentation phenotype impairs binding of the TFAP2A transcription factor that, together with the melanocyte master regulator MITF, regulates activity of the enhancer. Assays in zebrafish and mice reveal that IRF4 cooperates with MITF to activate expression of Tyrosinase (TYR), an essential enzyme in melanin synthesis. Our findings provide a clear example of a noncoding polymorphism that affects a phenotype by modulating a developmental gene regulatory network.

Requirements for Endothelin type-A receptors and Endothelin-1 signaling in the facial ectoderm for the patterning of skeletogenic neural crest cells in zebrafish

Genetic studies in mice and zebrafish have revealed conserved requirements for Endothelin 1 (Edn1) signaling in craniofacial development. Edn1 acts through its cognate type-A receptor (Ednra) to promote ventral skeletal fates and lower-jaw formation. Here, we describe the isolation and characterization of two zebrafish ednra genes - ednra1 and ednra2 -both of which are expressed in skeletal progenitors in the embryonic neural crest. We show that they play partially redundant roles in lower-jaw formation and development of the jaw joint. Knockdown of Ednra1 leads to fusions between upper- and lower-jaw cartilages, whereas the combined loss of Ednra1 and Ednra2 eliminates the lower jaw, similar to edn1-/-mutants. edn1 is expressed in pharyngeal arch ectoderm, mesoderm and endoderm. Tissue-mosaic studies indicate that, among these tissues, a crucial source of Edn1 is the surface ectoderm. This ectoderm also expresses ednrA1 in an edn1-dependent manner, suggesting that edn1 autoregulates its own expression. Collectively, our results indicate that Edn1 from the pharyngeal ectoderm signals through Ednra proteins to direct early dorsoventral patterning of the skeletogenic neural crest.

Expression of the zebrafish Staufen gene in the embryo and adult

Staufen, a double stranded RNA binding protein, has been shown to be involved in creating and maintaining cellular asymmetry in the Drosophila oocyte, neuroblast, and mammalian neuron. Staufen binds to the 3' UTR of specific mRNAs and acts in their localization and anchoring to various subcellular domains. Staufen's molecular interactions during development have been limited to investigations in Drosophila melanogaster. Since a vertebrate Staufen has not been studied in a developmental system, the aim of this study was to clone and characterize a staufen orthologue gene in the vertebrate developmental model, zebrafish. The zebrafish staufen-like sequence shows a 64% homology to the human staufen with a 81.2% homology in the highly conserved double stranded RNA binding domain (dsRBDs). Staufen maps on the LN54 radiation hybrid panel to linkage group 6, 16.25 cR from Z265 between fb22h06 and fi16e01. Northern blot and in situ hybridization showed that staufen is expressed both maternally and zygotically. Zygotically expressed staufen is localized to the developing nervous system and at 24 h is highly concentrated in the subventricular zone of the developing brain. Maternally expressed staufen is dispersed in the mature oocyte and early embryo. In the adult, staufen is expressed in specific brain nuclei, the testis, neurons and Leydig cells.

Sentence/vowel correlation in the evaluation of dysphonia

Considering the widespread use of the sustained vowel in the evaluation of voice disorders, our objective was to study the degree to which the vowel is representative of voice in continuous speech. Phonatory samples were recorded from 20 normal subjects and 60 patients representing commonly occurring voice problems (nodules, unilateral paralysis, and functional). The phonatory samples were evaluated by 25 listeners on the basis of 12 bipolar, semantic differential scales. Factor analysis produced two perceptual dimensions with similar loadings for both vowels and sentences. A correlation of 0.78 was obtained between vowels and sentences on factor 1 scores, "vocal severity," and a correlation of 0.77 was obtained between vowels and sentences on factor 2 scores, "pitch/quality." Six of the 80 pairs of sentences and vowels differed by two scale points or more on vocal severity. Results suggest that although a relatively strong relationship exists between the two measures, sustained vowel sounds may not be an adequate clinical index to the dysphonic severity of continuous speech.

Efficacy and safety of twice-daily augmented betamethasone dipropionate lotion versus clobetasol propionate solution in patients with moderate-to-severe scalp psoriasis

This 2-week, randomized, multicenter, investigator-blinded, parallel-group study was conducted to compare the efficacy and safety of augmented betamethasone dipropionate 0.05% lotion and clobetasol propionate 0.05% solution in the treatment of moderate-to-severe scalp psoriasis among 197 (193 assessable) healthy adult patients with at least 20% scalp-surface involvement. The patients received one of two treatments applied twice a day for 2 weeks. Signs and symptoms were evaluated at baseline, after 3 days (day 4), and after weeks 1 (day 8) and 2 (day 15) of treatment. As early as 3 days after treatment, scaling and induration were improved significantly faster by betamethasone dipropionate than by clobetasol propionate. Both treatments also reduced erythema and pruritus. Patients receiving betamethasone dipropionate had a significantly greater mean percent improvement in total sign/symptom scores (P < or = 0.015) at all visits and better mean global clinical response scores at the early visits (days 4 and 8) (P < or = 0.017). At the end of the study, only mild disease was present in both groups. Adverse events were reported by 34.0% and 36.4% of patients receiving betamethasone dipropionate and clobetasol propionate, respectively. All events were transient, most were mild and local, and no discontinuations resulted. The effects of treatment on the hypothalamic-pituitary-adrenal axis were not measured. In conclusion, augmented betamethasone dipropionate lotion and clobetasol propionate solution were equally effective, but betamethasone dipropionate lotion provided a faster onset of relief for scaling and induration, which may enhance patient compliance and patient satisfaction with treatment.

Acoustic prediction of severity in commonly occurring voice problems

The relative effectiveness of three acoustic measures (jitter, shimmer, and harmonic/noise ratio) in predicting the dysphonic severity of a diverse clinical population singly and together was investigated. Phonatory samples were recorded from 20 normal subjects and 60 patients representing 3 laryngeal groups (nodules, paralysis, and functional). The phonatory samples were evaluated by 22 listeners using a 7-point equal-appearing interval scale. Shimmer produced a bivariate correlation of 0.54 with dysphonic severity; harmonic/noise ratio correlated -0.32 with dysphonic severity; and jitter produced no significant correlation with severity. The combination of acoustic variables through multiple regression analysis produced a correlation of 0.56, with only shimmer and average F0 contributing to the correlation. For this particular clinical population, therefore, findings indicated that (a) none of the variables was strongly correlated with dysphonia ratings, and (b) a combination of acoustic predictors was no more successful than a single predictor of dysphonic severity, namely, shimmer.

Chemical cross-linking reveals a dimeric structure for CTP:phosphocholine cytidylyltransferase

CTP:phosphacholine cytidylyltransferase (EC 2.7.7.15) was purified from rat liver according to the method of Weinhold et al. (Weinhold, P. A., Rounsifer, M. E., and Feldman, D. A. (1986) J. Biol. Chem. 261, 5104-5110). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis with or without beta-mercaptoethanol revealed a single major band of 42,000 daltons. This band corresponds to the 45-kDa catalytic subunit isolated by Feldman and Weinhold (Feldman, D. A., and Weinhold, P. A. (1987) J. Biol. Chem. 262, 9075-9081). A minor component of 84,000 daltons was intensified in nonreducing gels when the sulfhydryl reducing agent, dithiothreitol, was removed from the enzyme preparation by dialysis. Reduction with dithiothreitol and electrophoresis in the second dimension showed that this 84-kDa protein was derived from the 42-kDa protein. This result suggested that the 42 kDa protein can be converted to an 84-kDa protein by disulfide bond formation. Reaction with the thiol-cleavable cross-linking reagents, dithiobis(succimidyl propionate) or dimethyl-3,3'-dithiobispropionimidate, converted the 42-kDa cytidylyltransferase subunit into a diffuse band approximately twice its molecular mass. Disulfide reduction and electrophoresis in the second dimension showed that this band was derived exclusively from the 42-kDa subunit. This cross-linking pattern was observed when cytidylyltransferase was bound to a Triton X-100 micelle or when bound to a membrane vesicle containing phosphatidylcholine, oleic acid, and Triton X-100. Reaction of the fully reduced enzyme with glutaraldehyde also generated a cross-linked dimer. All three cross-linking reagents inactivated the enzyme. Reduction of the disulfide cross-linkers with dithiothreitol partially reactivated the transferase. When Triton was removed from the enzyme preparation by DEAE-Sepharose chromatography, reaction of the detergent-depleted enzyme with glutaraldehyde generated a band corresponding to a hexamer and higher molecular weight aggregates. The dimeric form was regenerated by addition of either Triton X-100 or phosphatidylcholine-oleic acid vesicles. We conclude that the purified, native cytidylyltransferase, when bound to a detergent micelle or membrane vesicle, is a dimer composed of two noncovalently linked 42-kDa subunits. In the absence of a membrane or micelle, the dimers self-aggregate in a reversible manner.

Translocation of CTP: phosphocholine cytidylyltransferase from cytosol to membranes in HeLa cells: stimulation by fatty acid, fatty alcohol, mono- and diacylglycerol

Addition of oleate, oleyl alcohol, or palmitate to HeLa cell medium resulted in a rapid stimulation of PC synthesis and activation of CTP: phosphocholine cytidylyltransferase. Stimulation was optimal with 0.35 mM oleate, 0.3 mM oleyl alcohol and 5 mM palmitate, or 1 mM palmitate if EGTA were added to the medium. The cytidylyltransferase was activated by translocation of the inactive cytosolic form to membranes. In untreated cells approx. 30% of the total cytidylyltransferase was membrane bound, while in treated cells, 80-90% was membrane associated. Addition of bovine serum albumin (10 mg/ml) to cells previously treated with oleate (0.35 mM) rapidly removed cellular fatty acid, and the membrane-bound cytidylyltransferase activity returned to approx. 30%. Similar results were obtained by extraction of membranes with albumin in vitro. Although 95% of the free fatty acid was extracted, 30-40% of the membrane cytidylyltransferase remained bound. Translocation of cytidylyltransferase between isolated cytosol and microsomal fractions was promoted by addition of oleate, palmitate, oleyl alcohol, and monoolein. Addition of diacylglycerol, lysophosphatidylcholine, lysophosphatidylethanolamine, calcium palmitate, and detergents such as Triton X-100, cholate or Zwittergent did not stimulate translocation of the enzyme. Addition of oleoyl-CoA promoited translocation, however, 40% of it was hydrolyzed releasing free oleic acid. Cytosolic cytidylyltransferase bound to microsomes pre-treated with phospholipase C, which had 7-fold elevated diacylglycerol content. Fatty acid-promoted translocation was blocked by Triton X-100, but not by 1 M KCl. These results suggest that a variety of compounds with differing head group size and charge, and number of hydrocarbon chains can function as translocators, and that hydrophobic rather than ionic interactions mediate the binding of cytidylyltransferase to membranes.

Binding of CTP: phosphocholine cytidylyltransferase to large unilamellar vesicles

We have studied the binding of CTP: phosphocholine cytidylyltransferase from HeLa cell cytosol to large unilamellar vesicles of egg phosphatidylcholine (PC) or HeLa cell phospholipids that contain various amounts of oleic acid. A fatty acid/phospholipid molar ratio exceeding 10% was required for CTP: phosphocholine cytidylyltransferase binding to liposomes. At a fatty acid/phospholipid molar ratio of 1; 85% of the cytosolic CTP: phosphocholine cytidylyltransferase was bound. The enzyme also bound to liposomes with at least 20 mol% palmitic acid, monoolein, diolein or oleoylacetylglycerol. Oleoyl-CoA did not promote enzyme binding to liposomes. Binding to oleate-PC vesicles was blocked by Triton X-100 but not by 1 M KCl, and was reversed by incubation of the vesicles with bovine serum albumin. Cytidylyltransferase bound to egg PC vesicles that contained 33 mol% oleic acid equally well at 4 degrees C and 37 degrees C. The enzyme also bound to dimyristoyl- and dipalmitoylphosphatidylcholine vesicles containing oleic acid at temperatures below the phase transition for these liposomes. Binding of the cytidylyltransferase to egg PC vesicles containing oleic acid, monoolein, oleoylacetylglycerol or diolein resulted in enzyme activation, as did binding to dipalmitoylPC-oleic acid vesicles. However, binding to egg PC-palmitic acid vesicles did not fully activate the transferase. Various mechanisms for cytidylyltransferase interaction with membranes are discussed.

The supply of both CDP-choline and diacylglycerol can regulate the rate of phosphatidylcholine synthesis in HeLa cells

The incorporation of [methyl-14C]CDP-choline into phosphatidylcholine was measured in HeLa cells permeabilized with 0.125 mg digitonin/mL. The rate of phosphatidylcholine formation was influenced by the concentration of CDP-choline in the medium. The CDP-choline:1,2-diacylglycerol cholinephosphotransferase in permeabilized cells showed a Km of 88 microM for CDP-choline. A similar Km value of 104 microM was found for cholinephosphotransferase in microsomes isolated from HeLa cells when assayed in the presence of 2.4 mM dioleoylglycerol. In the absence of added diacylglycerol, the Km for CDP-choline for the microsomal cholinephosphotransferase was only 38 microM. The incorporation of [methyl-14C]CDP-choline into phosphatidylcholine was stimulated by the supply of diacylglycerol in both HeLa cells and isolated microsomes. A 2.4 mM dioleoylglycerol suspension increased cholinephosphotransferase activity fourfold in microsomes. The digitonin-treated cells were impermeable to the dioleoylglycerol suspension. Incubation of permeabilized cells with 150 microM acyl-CoA and 0.8 mM glycero-3-phosphate tripled cellular diacylglycerol levels, causing a doubling in the rate of phosphatidylcholine synthesis. A similar incubation of microsomes with acyl-CoA stimulated phosphatidylcholine synthesis twofold. Furthermore, incubation of microsomes with [3H]diacylglycerol and [14C]CDP-choline showed that both of the substrates were incorporated into phosphatidylcholine at the same rate. This result suggests that the stimulatory effects on cholinephosphotransferase arise from increases in the availability of substrates rather than activation of the enzyme. These results suggest that both in the permeabilized cells and in isolated membranes, the biosynthesis of phosphatidylcholine can be limited by both CDP-choline and diacylglycerol.

Solubilization and reconstitution of cholinephosphotransferase from sarcoplasmic reticulum: stabilization of solubilized enzyme by diacylglycerol and glycerol

Cholinephosphotransferase (CDPcholine: 1,2-diacylglycerol cholinephosphotransferase, EC 2.7.8.2), which catalyzes the terminal step in phosphatidylcholine synthesis via the CDPcholine pathway, is present in sarcoplasmic reticulum from rabbit skeletal muscle (Cornell, R. and MacLennan, D.H. (1985) Biochim. Biophys. Acta 835, 567-576). The conditions for solubilization and reconstitution of this enzyme were investigated as a preliminary step towards its eventual purification. The activity was not released by treatment of membranes with 1 M KCl, but was solubilized after dissolution of membranes with detergents. Cholinephosphotransferase was inactivated by cholate, deoxycholate, Triton X-100, octylglucoside, Tween-20 or SDS at concentrations which solubilize the membrane. However, the activity could be fully recovered after reconstituting the membrane by adding excess lipid (soybean) and removing detergent by gel filtration, dialysis or by absorption to Bio-Beads. When the membrane was solubilized with octylglucoside or cholate at weight ratios of detergent: membrane protein of at least 10, the activity was irreversibly lost unless stabilizers were added with detergent. The substrate diacylglycerol and glycerol were effective stabilizers.

The capacity of the sarcoplasmic reticulum for phospholipid synthesis: a developmental study

The activities of three enzymes involved in phospholipid synthesis, sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15), cholinephosphate cytidylyltransferase (EC 2.7.7.15), and cholinephosphotransferase (EC 2.7.8.2), were assayed in adult skeletal muscle. The acyltransferase and cholinephosphotransferase were concentrated in the sarcoplasmic reticulum, where their specific activities were 80 and 33%, respectively, of the specific activity in liver microsomes. Cytidylyltransferase activity was distributed throughout the cell with most of the activity in the cytosol. Its activity in muscle was only 10% of liver activity. Functional sarcoplasmic reticulum was isolated by density gradient centrifugation after calcium loading in the presence of phosphate. The specific activities of these enzymes wee undiminished in the calcium-loaded fraction, suggesting that these enzymes are intrinsic components of the sarcoplasmic reticulum. In developing muscle (2 and 6 days postnatal) acyltransferase and cholinephosphotransferase activities were also present in a calcium-loaded microsomal subfraction at the same level as in the adult. Cytidylyltransferase activity, on the other hand, was 8-fold higher in developing muscle. In addition, developing muscle had a 3-fold increase in the proportion of cytidylyltransferase associated with the microsomal fraction. These data suggest that sarcoplasmic reticulum has the capacity for phospholipid synthesis in mature and developing muscle, and that the rate of phosphatidylcholine synthesis may be regulated by the levels of cytidylyltransferase and by translocation of this enzyme between the sarcoplasmic reticulum and the cytosol.

Independent synthesis of phospholipid and the intrinsic proteins of the sarcoplasmic reticulum

The relationship between the synthesis of phospholipids and the intrinsic proteins of the sarcoplasmic reticulum was investigated in differentiating L6 cells in culture. The rates of lipid synthesis and turnover in L6 showed no large variations over the course of differentiation from myoblasts to myotubes while the rate of synthesis of the sarcoplasmic reticulum Ca2+-ATPase steadily increased. Removal of choline from the culture medium after the onset of fusion resulted in a 2-fold inhibition of phosphatidylcholine (PC) synthesis and a 40-50% reduction in total cellular PC content within 36 h. The synthesis and content of phosphatidylethanolamine also declined subsequent to the effect on PC. The amount of newly synthesized phospholipid in the microsomal fraction also decreased 50% in choline-deprived cells. Choline deprivation of myotubes for up to 4 days had no effect on the rates of synthesis of the Ca2+-ATPase or two intrinsic glycoproteins of 53,000 and 160,000 daltons. The newly synthesized proteins were incorporated into PC-deficient microsomal membranes. The synthesis of total cellular protein and total membrane protein was not altered, thus phospholipid:protein ratios declined 2-fold. These observations suggest that the assembly of the sarcoplasmic reticulum is not tightly coordinated with the rate of phospholipid synthesis.

Interrelated lipid alterations and their influence on the proliferation and fusion of cultured myogenic cells

We have cultured myogenic cells derived from primary explants and a cell line (L6) in a lipid-depleted medium (LDM) and produced large alterations of the fatty acyl and polar headgroup composition and of the cellular sterol levels. These alterations were produced by altering the composition of the media as follows: removing biotin and providing exogenous fatty acid; removing choline and providing exogenous ethanolamine or choline analogues; and by adding 25-OH cholesterol, an inhibitor of 3-hydroxy-3-methylglutarate (HMG)-CoA reductase. Relatively small, secondary alterations of other lipid classes accompany the large primary alteration. In general, they are not obviously compensatory for the primary alteration by retaining some physical property. We have explored the influence of these lipid alterations on myoblast proliferation and fusion into myotubes. In general, considerable variability appears tolerated, but there also appear to be limits. Long-term cultures grown in media containing a single fatty acid do not proliferate indefinitely, and the fatty acid does not become the sole fatty acyl component of the phospholipids. This phenomenon is also observed for cultures enriched in phosphatidylethanolamine (PE) or phosphatidyldimethylethanolamine (PDME). The influence of the lipid alterations on fusion is particularly interesting. The inclusion of 25-OH cholesterol inhibits fusion. Enrichment of the fatty acyl chains with elaidate or the polar headgroups with PE also inhibits fusion, but in contrast to that by 25-OH cholesterol, a significant fraction of the myoblasts are aligned and interacting with each other. Oleate enrichment enhances the rate of fusion.

Macromolecular absorption. Mechanism of horseradish peroxidase uptake and transport in adult and neonatal rat intestine

The immature small intestine of neonatal mammals is permeable to gamma globulins as a source of passive immunity. Allegedly, macromolecular absorption ceases when the epithelial cell membrane matures. However, some evidence exists that adult animals retain a limited capacity to transport antigenic and biologically active quantities of large molecules. In this study, the mechanism of absorption of the tracer protein, horseradish peroxidase (HRP), was tested in neonatal and adult rat gut sacs. Transport into serosal fluid was quantitated by enzymatic assay and monitored morphologically by histochemical techniques. A greater transport of HRP was noted in the adult jejunum compared to adult ileum and neonatal intestine. Morphologically, the uptake mechanism in adult intestine was similar to the endocytosis previously reported in neonatal animals Like other endocytotic processes, HRP uptake in adult rats is an energy-dependent process as determined by metabolic inhibitors and temperature-controlled studies. An understanding of the mechanism whereby macromolecules are bound to intestinal membranes and engulfed by them is necessary before the action of physiologic macromolecules such as enterotoxins can be appreciated.

Amygdalectomy and social behavior in the caged stump-tailed macaque (Macaca speciosa)

Species specific patterns of social behavior and environmental factors may be influential in determining the effects of amygdalectomy in subhuman primates. Amygdalectomy seems to produce less social disorganization in Macaca speciosa than in M. mulatto or Cercopithecus aetliiops. This may be related to their characteristically greater degree of positive social interactions than in the other species studied.