Arf-like GTPase Arl8b regulates lytic granule polarization and natural killer cell-mediated cytotoxicity

By exploiting NK cell LROs (known as lytic granules) as a model, a new role is defined for Arl8b in regulating motility and exocytosis of lytic granules of NK cells. Not only lytic granules but also the MTOC is unable to polarize toward the immune synapse formed between the NK cell and its target in Arl8b-depleted NK cells.

Natural killer (NK) lymphocytes contain lysosome-related organelles (LROs), known as lytic granules, which upon formation of immune synapse with the target cell, polarize toward the immune synapse to deliver their contents to the target cell membrane. Here, we identify a small GTP-binding protein, ADP-ribosylation factor-like 8b (Arl8b), as a critical factor required for NK cell–mediated cytotoxicity. Our findings indicate that Arl8b drives the polarization of lytic granules and microtubule-organizing centers (MTOCs) toward the immune synapse between effector NK lymphocytes and target cells. Using a glutathione S-transferase pull-down approach, we identify kinesin family member 5B (KIF5B; the heavy chain of kinesin-1) as an interaction partner of Arl8b from NK cell lysates. Previous studies showed that interaction between kinesin-1 and Arl8b is mediated by SifA and kinesin-interacting protein (SKIP) and the tripartite complex drives the anterograde movement of lysosomes. Silencing of both KIF5B and SKIP in NK cells, similar to Arl8b, led to failure of MTOC-lytic granule polarization to the immune synapse, suggesting that Arl8b and kinesin-1 together control this critical step in NK cell cytotoxicity.

Relevance of amyloid precursor-like protein 2 C-terminal fragments in pancreatic cancer cells

In some cellular systems, particularly neurons, amyloid precursor-like protein 2 (APLP2), and its highly homologous family member amyloid precursor protein (APP), have been linked to cellular growth. APLP2 and APP undergo regulated intramembrane proteolysis to produce C-terminal fragments. In this study, we found comprehensive expression of APLP2 C-terminal fragments in a panel of pancreatic cancer cell lines; however, APP C-terminal fragments were notably limited to the BxPC3 cell line. Extensive glycosaminoglycan modification on APLP2 was also found in the majority of pancreatic cancer cell lines. Glycosaminoglycan-modified and -unmodified APLP2, and particularly APLP2 C-terminal fragments, also demonstrated increased expression in oncogene-transformed pancreatic ductal cells. Additionally, elevated APLP2 levels were confirmed in human pancreatic cancer tissue. Downregulation of APLP2 and APP expression, alone or in combination, caused a decrease in the growth of a pancreatic cancer cell line with representatively low APP C-terminal fragment expression, the S2-013 cell line. Furthermore, we found that treatment with β-secretase inhibitors to block formation of APLP2 C-terminal fragments decreased the growth and viability of S2-013 cells, without affecting the survival of a non-transformed pancreatic ductal cell line. In conclusion, our studies demonstrate that abundant APLP2, but not APP, C-terminal fragment expression is conserved in pancreatic cancer cell lines; however, APP and APLP2 equally regulated the growth of S2-013 pancreatic cancer cells. Chiefly, our discoveries establish a role for APLP2 in the growth of pancreatic cancer cells and show that inhibitors preventing APLP2 cleavage reduce the viability of pancreatic cancer cells.

Analysis of major histocompatibility complex class I folding: novel insights into intermediate forms

Folding around a peptide ligand is integral to the antigen presentation function of major histocompatibility complex (MHC) class I molecules. Several lines of evidence indicate that the broadly cross-reactive 34-1-2 antibody is sensitive to folding of the MHC class I peptide-binding groove. Here, we show that peptide-loading complex proteins associated with the murine MHC class I molecule K(d) are found primarily in association with the 34-1-2(+) form. This led us to hypothesize that the 34-1-2 antibody may recognize intermediately, as well as fully, folded MHC class I molecules. To further characterize the form(s) of MHC class I molecules recognized by 34-1-2, we took advantage of its cross-reactivity with L(d) . Recognition of the open and folded forms of L(d) by the 64-3-7 and 30-5-7 antibodies, respectively, has been extensively characterized, providing us with parameters against which to compare 34-1-2 reactivity. We found that the 34-1-2(+) L(d) molecules displayed characteristics indicative of incomplete folding, including increased tapasin association, endoplasmic reticulum retention, and instability at the cell surface. Moreover, we show that an L(d) -specific peptide induced folding of the 34-1-2(+) L(d) intermediate. Altogether, these results yield novel insights into the nature of MHC class I molecules recognized by the 34-1-2 antibody.

Regulation of major histocompatibility complex class I molecule expression on cancer cells by amyloid precursor-like protein 2

The three members of the amyloid precursor protein family in mammals [amyloid precursor protein, amyloid precursor-like protein 1, and amyloid precursor-like protein 2 (APLP2)] have been implicated in a large array of intracellular processes, which include development, transcription, apoptosis, metabolism, and the cell cycle. A series of studies by our laboratories has demonstrated that APLP2 is highly expressed by many cancer cell lines (with the highest expression in pancreatic cancer cell lines) and that it facilitates major histocompatibility complex (MHC) class I molecule endocytosis. This review focuses on this recently revealed function of APLP2 relevant to tumor immunology: that it acts as a novel regulator of MHC class I molecule surface expression.

Physical and dental manifestations of oral-facial-digital syndrome type I

Oral-facial-digital (OFD) syndrome is the collective name of a group of rare inherited syndromes characterized by malformations of the face, oral cavity, hands and feet. OFD syndrome type I, also known as the Papillon-League-Psaume syndrome warrants our attention because early diagnosis from an odontologic viewpoint will minimize the sequalae of developing physical and dental abnormalities. The present article highlights the clinical as well as the radiographic findings and the treatment that was done of a 10-year-old girl child diagnosed with OFD I.

Invariant natural killer T cells recognize lipid self antigen induced by microbial danger signals

Invariant natural killer T cells (iNKT cells) have a prominent role during infection and other inflammatory processes, and these cells can be activated through their T cell antigen receptors by microbial lipid antigens. However, increasing evidence shows that they are also activated in situations in which foreign lipid antigens would not be present, which suggests a role for lipid self antigen. We found that an abundant endogenous lipid, β-D-glucopyranosylceramide (β-GlcCer), was a potent iNKT cell self antigen in mouse and human and that its activity depended on the composition of the N-acyl chain. Furthermore, β-GlcCer accumulated during infection and in response to Toll-like receptor agonists, contributing to iNKT cell activation. Thus, we propose that recognition of β-GlcCer by the invariant T cell antigen receptor translates innate danger signals into iNKT cell activation.

Lysosomal trafficking, antigen presentation, and microbial killing are controlled by the Arf-like GTPase Arl8b

Antigen presentation and microbial killing are critical arms of host defense that depend upon cargo trafficking into lysosomes. Yet, the molecular regulators of traffic into lysosomes are only partly understood. Here, using a lysosome-dependent immunological screen of a trafficking shRNA library, we identified the Arf-like GTPase Arl8b as a critical regulator of cargo delivery to lysosomes. Homotypic fusion and vacuole protein sorting (HOPS) complex members were identified as effectors of Arl8b and were dependent on Arl8b for recruitment to lysosomes, suggesting that Arl8b-HOPS plays a general role in directing traffic to lysosomes. Moreover, the formation of CD1 antigen-presenting complexes in lysosomes, their delivery to the plasma membrane, and phagosome-lysosome fusion were all markedly impaired in Arl8b silenced cells resulting in corresponding defects in T cell activation and microbial killing. Together, these results define Arl8b as a key regulator of lysosomal cellular and immunological functions.

Increased expression and cleavage of amyloid precursor-like protein 2 in pancreatic cancer and regulation of fragment stability by major histocompatibility complex class I molecules (165.4)

Particularly in neurological systems, amyloid precursor-like protein 2 (APLP2) has been linked to cellular growth, adhesion and migration. Our laboratory has demonstrated that several human pancreatic cancer cell lines, as well as pancreatic cancer tissue, express a high level of APLP2. Furthermore, we showed that oncogene-induced transformation of pancreatic cells resulted in increased levels of full-length APLP2 and 12-15 kDa APLP2 C-terminal cleavage fragments. Additionally, in pancreatic cancer cell lines we have noted association of APLP2 C-terminal fragments and major histocompatibility complex (MHC) class I molecules, the proteins responsible for the presentation of tumor antigens. The APLP2 C-terminal fragments associated with MHC class I molecules had prolonged stability compared to unassociated fragments. Incubation with calyculin A, which enhances serine/threonine phosphorylation, increased the rate of APLP2 C-terminus turnover. In agreement with our earlier finding, the APLP2 C-termini associated with MHC class I molecules underwent relatively slower degradation in the presence of calyculin A. Thus, MHC class I molecules have a previously unrecognized function of regulating APLP2 homeostasis. Overall, our discoveries have established that APLP2 expression and cleavage are up-regulated in pancreatic cancer, and have led to a new understanding of the involvement of MHC class I molecules in the regulation of APLP2 C-terminal fragments in pancreatic cancer cells.

Serologic analysis of MHC class I folding intermediates (100.9)

During the process of peptide selection, MHC class I molecules transition from an open, peptide-free conformer to a folded, peptide-bound state. Thus, MHC class I molecules have been proposed to adopt an intermediate conformation during peptide binding; however, the molecular nature of this transition state is unknown. Here, we report evidence that the 34-1-2 antibody, which recognizes several murine MHC class I molecules, is able to distinguish an intermediately folded conformer. The majority of 34-1-2+ Ld molecules were found to represent a distinct pool of MHC class I molecules that were not recognized by the anti-folded Ld antibody 30-5-7. Moreover, 34-1-2+ Ld molecules were found to display characteristics indicative of incomplete folding, including increased tapasin association and endoplasmic reticulum (ER) retention. Additionally, our data suggest that tapasin associates with sub-optimally loaded 34-1-2+ Kd molecules and may facilitate the retrieval of these molecules to the ER. We have designated this MHC class I conformation as 34-1-2-INT (34-1-2+, intermediately folded). Together with prior knowledge regarding the 34-1-2 epitope, our analysis supports a model whereby binding of the peptide N-terminus permits MHC class I molecules to adopt an intermediately folded conformation which subsequently converts to the fully folded form upon optimization of C-terminal interactions. Thus, the 34-1-2 antibody is an important tool in understanding MHC class I peptide loading.

Early childhood caries and oral rehabilitation. A treatment quandary

Early childhood caries (ECC) is a virulent form of dental caries that can destroy the primary dentition of toddlers and preschool children. It occurs worldwide, afflicting predominantly disadvantaged children. Although Streptococcus mutans is the most likely causative agent, diet also plays a critical role in the acquisition and clinical expression of this infection. Early acquisition of S. mutans via vertical or horizontal transmission is a key event in the natural history of the disease that coupled with caries promoting feeding behaviours results in accumulation of these organisms to levels exceeding 30% of the total cultivable plaque flora, which in turn leads to rapid demineralization of the tooth structure. Inflicted children may also have other associated health problems, ranging from local infections to oral pain that manifest as difficulty in eating and sleeping, reduced growth and altered behaviour. Oral rehabilitation usually consists of restoration or surgical removal of carious teeth along with recommendations regarding feeding habits. Although treatment can be instituted in the dental clinic, it becomes costly sometimes when cooperative capacity of babies and preschool children necessitates the use of general anaesthesia. Primary prevention of ECC has largely been restricted to counselling parents regarding proper feeding behaviour, oral hygiene measures and new strategies that address the infectious component through use of topical antimicrobial therapy in order to defeat this common oral affliction.

Influence of intermolecular disulfide bonds on assembly of mouse MHC class I molecules (130.25)

Within the major histocompatibility (MHC) class I peptide-loading complex, tapasin and ERp57 are joined by a stable disulfide bond which is necessary for the efficient assembly of MHC class I molecules. In our investigation of murine tapasin, we identified a large covalently bound complex involving wild type mouse tapasin and ERp57. This complex, which migrates at ~150 kDa, is noticeably larger than the 110 kDa tapasin-ERp57 complex previously identified in human cells. Additional data suggest that the mouse MHC class I molecule Kd may be a part of this ~150 kDa complex. In order to investigate the importance of tapasin-ERp57 disulfide bonding for the assembly of murine MHC class I molecules, we introduced a tapasin C95S mutant into tapasin knockout mouse fibroblasts. Although this tapasin mutant is unable to disulfide bond with ERp57, mouse tapasin C95S was found to maintain a non-covalent association with ERp57. Mutation of tapasin C95 impaired the maturation and stability of MHC class I Kd molecules to a greater extent than was previously observed for the human MHC class I molecule, B*4402. Furthermore, the maturation and stability of mouse MHC class I Kb molecules was also impaired in cells expressing mouse tapasin C95S. In total, these results highlight inter-species differences in the MHC class I assembly pathway and emphasize the importance of studying diverse MHC class I allotypes.

Monopolar diathermy used for correction of ankyloglossia

Tongue tie, also known as ankyloglossia or ankyloglossia inferior, is a relatively common finding in pediatric surgical outpatient clinics. It occurs as a result of a short, tight, lingual frenum causing tethering of the tongue tip. It is a common oral finding in infants and children, which is often neglected. Although most cases resolve or are asymptomatic, some patients develop articulation problems and other concerns related to poor tongue-tip mobility. In this article, we report on a 5-year old girl with a tongue tie, who underwent frenectomy using monopolar diathermy under local anesthesia without any postoperative complication.

Mechanism for amyloid precursor-like protein 2 enhancement of major histocompatibility complex class I molecule degradation

Earlier studies have demonstrated interaction of the murine major histocompatibility complex (MHC) class I molecule K(d) with amyloid precursor-like protein 2 (APLP2), a ubiquitously expressed member of the amyloid precursor protein family. Our current findings indicate that APLP2 is internalized in a clathrin-dependent manner, as shown by utilization of inhibitors of the clathrin pathway. Furthermore, we demonstrated that APLP2 and K(d) bind at the cell surface and are internalized together. The APLP2 cytoplasmic tail contains two overlapping consensus motifs for binding to the adaptor protein-2 complex, and mutation of a tyrosine shared by both motifs severely impaired APLP2 internalization and ability to promote K(d) endocytosis. Upon increased expression of wild type APLP2, K(d) molecules were predominantly directed to the lysosomes rather than recycled to the plasma membrane. These findings suggest a model in which APLP2 binds K(d) at the plasma membrane, facilitates uptake of K(d) in a clathrin-dependent manner, and routes the endocytosed K(d) to the lysosomal degradation pathway. Thus, APLP2 has a multistep trafficking function that influences the expression of major histocompatibility complex class I molecules at the plasma membrane.

Comparative analysis of the impact of a free cysteine in tapasin on the maturation and surface expression of murine MHC class I allotypes

Tapasin is a key molecule in the major histocompatibility complex (MHC) class I peptide-loading complex, interacting with several other proteins in the complex. An amino acid substitution at a free cysteine position in tapasin has been shown to disrupt the covalent association of tapasin with ERp57. In this study, we mutated the free cysteine in mouse tapasin, and analysed the effects on the cell surface expression of the mouse MHC class I molecules K(d) and K(b). The C95S substitution in mouse tapasin increased the proportion of open forms relative to folded forms for both types of MHC class I molecules at the cell surface. Furthermore, the C95S substitution resulted in increased association of tapasin with folded K(d). Overall, our studies with these mouse MHC class I allotypes have revealed that the free cysteine 95 in mouse tapasin influences stable expression at the plasma membrane for both MHC class I allotypes, and have shown that tapasin's interaction with folded K(d) is elevated by the C95S substitution in tapasin.

APLP2 Diverts MHC-Peptide Complexes to Clathrin-Mediated Endocytosis and Lysosomal Degradation (78.14)

The amyloid precursor-like protein 2 (APLP2) is a secreted protein that is ubiquitously expressed. We have shown previously that APLP2 associates with peptide-bound forms of H-2Kd, and influences the endocytosis, surface expression, stability, and turnover of Kd. Our new findings indicate that APLP2 is internalized in a clathrin-dependent manner, as a dominant negative dynamin II mutant and the C-terminal tail of AP180 (both inhibitors of clathrin-dependent endocytosis) block its internalization. However, endocytosis of Kd is not blocked by these inhibitors, consistent with findings by others that MHC class I molecules are internalized mainly through a clathrin-independent pathway. Furthermore, the APLP2 cytoplasmic tail contains overlapping tyrosine-based motifs that can potentially bind to adaptor protein AP-2. Mutation of the tyrosine in this sequence severely impaired endocytosis of APLP2. This APLP2 mutant, unlike wild-type APLP2, failed to enhance the endocytosis of Kd molecules. Also, we found that APLP2 and Kd bind at the plasma membrane (PM) and are internalized together. Upon increased APLP2 expression, Kd molecules were predominantly directed to the lysosomes rather than recycled to the PM. These findings suggest a model in which APLP2 binds Kd at the PM, facilitates uptake of Kd in a clathrin-dependent manner, and routes the endocytosed Kd to the lysosomal degradation pathway. Thus, APLP2 has a multi-step trafficking function which influences the expression of MHC-peptide complexes at the PM. [NIH GM57428 & GM74876]

Amyloid precursor-like protein 2 association with HLA class I molecules

Amyloid precursor-like protein 2 (APLP2) is a ubiquitously expressed protein. The previously demonstrated functions for APLP2 include binding to the mouse major histocompatibility complex (MHC) class I molecule H-2K(d) and down regulating its cell surface expression. In this study, we have investigated the interaction of APLP2 with the human leukocyte antigen (HLA) class I molecule in human tumor cell lines. APLP2 was readily detected in pancreatic, breast, and prostate tumor lines, although it was found only in very low amounts in lymphoma cell lines. In a pancreatic tumor cell line, HLA class I was extensively co-localized with APLP2 in vesicular compartments following endocytosis of HLA class I molecules. In pancreatic, breast, and prostate tumor lines, APLP2 was bound to the HLA class I molecule. APLP2 was found to bind to HLA-A24, and more strongly to HLA-A2. Increased expression of APLP2 resulted in reduced surface expression of HLA-A2 and HLA-A24. Overall, these studies demonstrate that APLP2 binds to the HLA class I molecule, co-localizes with it in intracellular vesicles, and reduces the level of HLA class I molecule cell surface expression.

Influence of the tapasin C terminus on the assembly of MHC class I allotypes

Several endoplasmic reticulum proteins, including tapasin, play an important role in major histocompatibility complex (MHC) class I assembly. In this study, we assessed the influence of the tapasin cytoplasmic tail on three mouse MHC class I allotypes (H2-K(b), -K(d), and -L(d)) and demonstrated that the expression of truncated mouse tapasin in mouse cells resulted in very low K(b), K(d), and L(d) surface expression. The surface expression of K(d) also could not be rescued by human soluble tapasin, suggesting that the surface expression phenotype of the mouse MHC class I molecules in the presence of soluble tapasin was not due to mouse/human differences in tapasin. Notably, soluble mouse tapasin was able to partially rescue HLA-B8 surface expression on human 721.220 cells. Thus, the cytoplasmic tail of tapasin (either mouse or human) has a stronger impact on the surface expression of murine MHC class I molecules on mouse cells than on the expression of HLA-B8 on human cells. A K408W mutation in the mouse tapasin transmembrane/cytoplasmic domain disrupted K(d) folding and release from tapasin, but not interaction with transporter associated with antigen processing (TAP), indicating that the mechanism whereby the tapasin transmembrane/cytoplasmic domain facilitates MHC class I assembly is not limited to TAP stabilization. Our findings indicate that the C terminus of mouse tapasin plays a vital role in enabling murine MHC class I molecules to be expressed at the surface of mouse cells.

Effect of invariant chain on major histocompatibility complex class I molecule expression and stability on human breast tumor cell lines

Invariant chain (Ii) binds to the human leukocyte antigen (HLA) class II molecule and assists it in the process of peptide acquisition. In addition, Ii binds to the HLA class I molecule, although there has been little study of its effects on the HLA class I molecule. In addition to its normal expression on antigen-presenting cells, Ii expression is up regulated in a variety of tumors. By flow cytometric analysis, we found that expression of Ii resulted in an increase in the number of cell surface HLA class I molecules and in the proportion of unstable HLA class I molecules at the surface of breast tumor cell lines. These data suggest that the expression of Ii by tumor cells may quantitatively and qualitatively alter the presentation of antigens on those cells.

Amyloid precursor-like protein 2 increases the endocytosis, instability, and turnover of the H2-K(d) MHC class I molecule

The defense against the invasion of viruses and tumors relies on the presentation of viral and tumor-derived peptides to CTL by cell surface MHC class I molecules. Previously, we showed that the ubiquitously expressed protein amyloid precursor-like protein 2 (APLP2) associates with the folded form of the MHC class I molecule K(d). In the current study, APLP2 was found to associate with folded K(d) molecules following their endocytosis and to increase the amount of endocytosed K(d). In addition, increased expression of APLP2 was shown to decrease K(d) surface expression and thermostability. Correspondingly, K(d) thermostability and surface expression were increased by down-regulation of APLP2 expression. Overall, these data suggest that APLP2 modulates the stability and endocytosis of K(d) molecules.

The effects of magnetic field on the biomechanics parameters of soleus and extensor digitorum longus muscles in rats with streptozotocin-induced diabetes

BACKGROUND

The aim of this study was to determine the effects of the magnetic field (MF) on the isometric contractile characteristics of the soleus and extensor digitorum longus (EDL) muscles in rats both with and without diabetes.

METHODS

Biomechanical parameters were recorded in vitro from Wistar rats without diabetes (Group I, n=20), rats without diabetes exposed to MF (Group II, n=20), rats with streptozotocin-induced diabetes (Group III, n=20), and rats with diabetes exposed to MF (Group IV, n=20). Muscle strips were taken from the distal tendon soleus and EDL muscles of rats killed by decapitation. The muscles were hung in organ baths containing Krebs solution (pH 7.4) with a gas mixture of 95% O2 and 5% CO2. Then the muscles were triggered to direct supramaximal stimulation with 0.05 Hz frequency square pulses for periods of 0.5 ms to obtain control values. The contractile parameters were also determined for two muscles of the four groups. Later, the tension-frequency relationship was determined by applying stimulating pulses of 10, 20, 50, and 100 Hz to the muscles.

RESULTS

Diabetes caused a certain amount of decrease in the contractile force of the two muscles compared with that of control values. However, MF increased the contractile force of the two muscles in rats both with and without diabetes. The isometric contraction forces obtained by different stimulating frequencies showed a significant linear increase in the tetanic contraction (P<0.05). Diabetes increased the contraction time of the isometric twitch tension compared with that of the control group with a statistically significant difference (P<0.05). MF decreased the contraction time of the two muscles of rats without diabetes (P<0.05) but increased that of rats with diabetes (P>0.05).

CONCLUSION

In our study, these results suggest that MF exposure regulates the isometric contractile characteristics of the soleus and EDL muscles of rats with diabetes, positively.

CCL21 is an effective surgical neoadjuvant for treatment of mammary tumors

In previous studies, the chemokine CCL21 has shown biological activities that include T cell, natural killer (NK) cell, and dendritic cell (DC) chemoattraction. The goal of this study was to determine the effects of administering CCL21 to orthotopic mammary tumors in terms of impact on tumor growth rate, immune cell infiltration of the primary tumor and survival. We found that a single intratumoral administration of CCL21 slowed the growth of orthotopic mammary tumors and increased intratumoral infiltration by T cells, NK cells and DCs. CCL21 intratumoral administration also prolonged the survival of tumor-earing mice. Furthermore, mice that received intratumoral neoadjuvant CCL21 ior to surgical resection of tumors survived significantly longer than control mice. The urviving neoadjuvant CCL21-reated mice, when challenged again with cl-6, had significantly slower rate of tumor growth than challenged control mice. Thus, our ata indicate that CCL21 treatment prior to mammary tumor resection can significantly rolong survival and increase resistance to subsequent tumor challenge. Overall, our indings suggest that intratumoral administration of CCL21 has potential as a neoadjuvant mmunotherapy for breast cancer.

Similarities and differences in tapasin interaction with disparate murine MHC class I allotypes (93.11)

Tapasin is a key molecule in the major histocompatibility complex (MHC) class I peptide-loading complex. In this study, we first assessed the influence of the tapasin C-terminus on H2-Kb, -Kd, and -Ld in mouse cells. Truncated mouse tapasin (lacking the transmembrane and C-terminal region) was unable to associate with TAP or any of three murine MHC class I allotypes, and did not assist murine MHC class I folding and surface expression. A tapasin mutant with a single substitution in the C-terminus (K408W) increased the amount of Kd (but not Ld) in the open, peptide-free form, relative to wild type tapasin. We investigated whether Kd was also particularly responsive to other tapasin mutations, and found that a C95S substitution in tapasin also caused an elevation in open Kd (but not open Ld or Kb). Folded Kd was found to be amply present in association with wild type tapasin, and even more so with tapasin K408W and C95S. In summary, our results suggest that the C-terminus of mouse tapasin plays a vital role in the surface expression of murine MHC class I molecules, and that mouse MHC allotypes vary in their sensitivity to specific alterations in tapasin sequence and in their release from tapasin after folding. Overall, our results reveal new complexity in tapasin’s interactions with polymorphic MHC class I molecules. (NIH Grant GM57428)

Regulation of Antigen Presentation by Amyloid Precursor-Like Protein 2 (36.1)

The amyloid precursor-like protein 2 (APLP2) is a secreted protein that is ubiquitously expressed. We have found that APLP2 over-expression decreases the quantity of H2-Kd molecules on the plasma membrane. In addition, Kd thermostability was improved by APLP2 down-regulation, suggesting that APLP2 affects Kd peptide selection and/or retention. The effects of APLP2 on Kd are likely related to their physical association, as pulse-chase experiments demonstrated interaction for up to two hours after Kd synthesis. Furthermore, significant co-localization of Kd molecules with APLP2 was observed in vesicular structures both at steady state and during endocytosis of Kd molecules from the cell surface. Mutagenesis studies revealed that APLP2/MHC association is influenced by sequences in the peptide-binding region and the α3 domain of the MHC class I heavy chain. β2m has an impact on APLP2/MHC interaction, since introduction of human β2m into mouse fibroblasts increased the level of interaction between H2-Dd and APLP2. In summary, APLP2 affects MHC class I cell surface expression and thermostability by an interaction controlled by more than one domain of the MHC class I heavy chain and by β2m. These data support a model in which APLP2 regulates MHC class I trafficking, and thereby antigen presentation. (NIH Grants AI54645, GM57428, and GM74876)

Unusual features associated with cranial openings of optic canal in dry adult human skulls

One hundred and eighty six dry adult human skulls (372 sides) were studied in order to reveal the presence of unusual features--such as recess, fissure and notch--in the cranial opening of the optic canal. Recess, an extension of the lateral wall, was found in 229 (61.5%) sides. Fissure, an irregular discontinuity above the lateral recess, was observed in 158 (42.4%) sides. Notch, a gap in the posterior-most limit of the roof, was seen in 66 (17.7%) sides. These were commonly seen bilaterally. The etiology of these was attributed to the development of the optic canal. During intrauterine life the optic canal is in the form of a large keyhole shaped foramen, which slowly transforms into the adult canal. A developmental arrest at an early stage may lead to the formation of recesses and fissures.