Chromosome 18 suppresses prostate cancer metastases

Loss of heterozygosity and allelic imbalance data has shown that there are two distinct regions of loss on chromosome 18q associated with the progression of prostate cancer (CaP). To investigate the functional significance of chromosome 18q loci in CaP, we utilized the technique of microcell-mediated chromosome transfer to introduce an intact chromosome 18 into the human prostate cancer cell line, PC-3. Three of the resulting hybrid lines were compared to the PC-3 cells in vitro and in vivo. The hybrid cell lines, containing an intact copy of the introduced chromosome 18, exhibited a substantial reduction in anchorage-dependent and independent growth in vitro. These hybrid cell lines also made smaller tumors in nude mice following subcutaneous injection compared to PC-3 cells. Because tumor growth was not completely eliminated by introduction of chromosome 18, we assessed the ability of the hybrids to metastasize to bone after intra-cardiac inoculation in a nude mouse model. Mice inoculated with PC-3 hybrids containing intact copies of chromosome 18 had significantly fewer bone metastases and dramatically improved survival compared to PC-3 cells. In addition, the introduction of chromosome 18 significantly reduced tumor burden in extraskeletal sites. This was not because of differences in growth rates because mice bearing hybrids were monitored for metastases over twice as long as mice bearing PC-3 cells. Taken together, these data suggest that chromosome 18 has a functional role in CaP to suppress growth and metastases. Identification of the responsible gene(s) may lead to molecular targets for drug discovery.

Parathyroid hormone-related protein (PTHrP)-(1-139) isoform is efficiently secreted in vitro and enhances breast cancer metastasis to bone in vivo

Parathyroid hormone-related peptide (PTHrP) is a mediator of local osteolysis due to breast cancer. Three isoforms of PTHrP, (1-139), (1-141), and (1-173), are products of alternative splicing in humans, but the specific contribution of each of these isoforms to osteolytic metastasis caused by breast cancer has not been evaluated. To determine the role of PTHrP isoforms in breast cancer metastasis to bone, the human breast cancer cell line MDA-MB-231 (MDA-231) was stably transfected with cDNAs for human prepro PTHrP-(1-139), -(1-141), or -(1-173). Stable MDA/PTHrP-(1-139) clones expressed more PTHrP mRNA and secreted more PTHrP protein, compared with MDA/PTHrP-(1-141), -(1-173), or parental MDA-231. Parental MDA-231 cells and clones expressing each isoform had similar growth rates in vitro. In a mouse model of bone metastases, the osteolytic lesion area of radiographs was greatest in mice bearing MDA/PTHrP-(1-139) compared with those bearing MDA/PTHrP-(1-141), -(1-173), or parental MDA-231. Ca(++) and plasma PTHrP concentrations were significantly higher in the MDA/PTHrP-(1-139) compared with the MDA/PTHrP-(1-141), -(1-173), or parental MDA-231 groups. These data demonstrate that the PTHrP-(1-139) isoform was produced to a greater extent than PTHrP-(1-141) or -(1-173), and in vivo enhanced osteolysis with increased plasma PTHrP concentrations and hypercalcemia compared with overexpression of PTHrP-(1-141) or -(1-173).

Establishment of an osteoid preosteocyte-like cell MLO-A5 that spontaneously mineralizes in culture

The mechanisms controlling the initiation of mineralization of bone matrix are not clear. To examine this process, we established a cell line called MLO-A5 that mineralizes in sheets, not nodules, within 3 days of culture in the presence of beta-glycerophosphate (beta-GP) and ascorbic acid and within 7 days in the absence of beta-GP and ascorbic acid. The mineral formed in both cases was shown to be bonelike apatite by Fourier transformed infrared (FTIR) spectroscopy. Mineral-to-matrix ratios (min/matrix) calculated from the FTIR data, which are related directly to ash weight, were approximately 0.4 in the absence of beta-GP and ascorbic acid and approximately 1.2 in the presence of beta-GP and ascorbic acid. By comparison, these ratios in fetal rat calvarial cells without beta-GP equal 0 and with beta-GP 1.9. This cell line and three others (MLO-A2, -D1, and -D6) were isolated from the long bones of transgenic mice expressing the large T-antigen driven by the osteocalcin promoter, the same mice from which the osteocyte-like cell line MLO-Y4 was isolated.(1) The cell lines were selected based on a dendritic or stellate morphology. MLO-A5 cells express high alkaline phosphatase, collagen type 1, parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) receptor, bone sialoprotein (BSP), and osteocalcin (767 ng/10(6) cells compared with <1-2.2 ng/10(6) cell for primary mouse osteoblasts and five osteoblast cell lines). The single unique feature of the MLO-A5 cells compared with the other three nonmineralizing cell lines is the high expression of messenger RNA (mRNA) for BSP. These cell lines may represent stages of osteocyte differentiation and the MLO-A5 cells represent the postosteoblast, preosteocyte responsible for triggering mineralization of osteoid.

Ibandronate decreases bone disease development and osteoclast stimulatory activity in an in vivo model of human myeloma

The benefits of bisphosphonate therapy for multiple myeloma bone disease have been clearly documented. However, the effects of bisphosphonates on the osteoclast stimulatory activity (OSA) that is present in the marrow of patients with multiple myeloma, even before the bone disease is detectable, are unknown. Therefore, we examined the effects of ibandronate (IB) treatment prior to the development of bone disease in a murine model of human myeloma. Sublethally irradiated severe combined immunodeficient (SCID) mice were transplanted with ARH-77 cells on day 0. These ARH-77 mice were treated daily with subcutaneous injections of IB started before or at different times after tumor injection as follows: group 1 was started on day -7; group 2 on day 0; group 3 on day +7; group 4 on day +14 after IB administration; and group 5 (control) received no IB. Mice were sacrificed after they developed paraplegia. The onset of paraplegia was delayed in group 1 vs all other groups (mean day 27 vs day 32; p = 0.0098). The number of lytic lesions and the bone surface area of resorption (mm(2)) were significantly decreased in groups 1, 2, and 3, which were treated early with IB, when compared with groups 4 and 5 (p = 0.003 and 0.002, respectively). OSA, as measured by the capacity of bone marrow plasma from ARH-77 mice to induce osteoclast (OCL) formation in human bone marrow cultures, was decreased proportionally to the length of IB treatment. Group 1 had the lowest OSA compared with the other groups (p = 0.003). However, all mice eventually developed paraplegia, and at time of sacrifice, tumor burden was not grossly different among the groups. Interestingly, macroscopic abdominal tumors were more frequent in mice treated with IB. These data demonstrate that early treatment of ARH-77 mice with IB prior to development of myeloma bone disease decreases OSA and possibly retards the development of lytic lesions, but not eventual tumor burden.

Low cell motility induced by hsp27 overexpression decreases osteolytic bone metastases of human breast cancer cells in vivo

The mechanisms controlling the formation of osteolytic bone metastases in patients with breast cancer are still poorly understood. To explore the role of motility in the establishment of osteolytic bone metastases, we have used a model of bone metastasis in which MDA-MB-231 breast cancer cells exhibiting low (hsp27-transfectants) and high (control-transfectant) endogenous cell motility were compared. We found that MDA-MB-231 cells exhibiting low cell motility were less capable of establishing osteolytic lesions. The number and the area of the osteolytic lesions in mice inoculated with low motility cells were both significantly smaller. Histomorphometry of bone lesions also demonstrated less tumor area in mice bearing hsp27 transfectants although there was no difference in the osteoclast number per square millimeter of tumor-bone interface. These data suggest that cell motility may be an important mechanism in the metastatic cascade of breast cancer cells to the bone and that controlling cell motility may be a useful target to prevent the establishment of osteolytic bone metastases.

Avian osteoclast cells are stimulated to resorb calcified matrices by and possess receptors for leukotriene B4

Leukotriene B4 (LTB4) is elevated in inflammatory conditions and appears to be a potential mediator of inflammation. We have recently shown that this 5-lipoxygenase metabolite of arachidonic acid stimulates bone resorption in vitro and in vivo. In order to determine the mechanism whereby LTB4 causes bone resorption, avian osteoclasts were examined for the effects of LTB4 and for the presence of LTB4 receptors. Isolated avian osteoclast mononuclear precursor cells, which fuse in culture to form multinucleated cells, were chosen for receptor binding studies because this population is a morphologically similar source of osteoclasts, and large numbers of these cells can be obtained from egg-laying hens. Binding of LTB4 and activation would support the hypothesis of a direct effect of this compound on osteoclasts. LTB4 stimulated isolated avian osteoclasts to form resorption lacunae on calcified matrices and to increase their content of tartrate-resistant acid phosphatase (TRAP), a marker of activated osteoclasts. Receptor binding studies were performed at day 1, when the cells were mononuclear, at day 4, when mononuclear precursors were actively fusing, and at day 7, when fusion has slowed. Scatchard analysis of saturation binding data showed two classes of binding sites, a high- and low-affinity binding site with dissociation constants (KD) of 0.2-0.4 nM and 5. 6-24 nM. Association studies showed rapid binding of LTB4 to the cells within 10 minutes. These data show that LTB4 accelerates fusion and activates highly enriched populations of avian osteoclasts and that LTB4 receptors are present in this cell population.

TGF-beta signaling blockade inhibits PTHrP secretion by breast cancer cells and bone metastases development

Breast cancer frequently metastasizes to the skeleton, and the associated bone destruction is mediated by the osteoclast. Growth factors, including transforming growth factor-beta (TGF-beta), released from bone matrix by the action of osteoclasts, may foster metastatic growth. Because TGF-beta inhibits growth of epithelial cells, and carcinoma cells are often defective in TGF-beta responses, any role of TGF-beta in metastasis is likely to be mediated by effects on the surrounding normal tissue. However, we present evidence that TGF-beta promotes breast cancer metastasis by acting directly on the tumor cells. Expression of a dominant-negative mutant (TbetaRIIDeltacyt) of the TGF-beta type II receptor rendered the human breast cancer cell line MDA-MB-231 unresponsive to TGF-beta. In a murine model of bone metastases, expression of TbetaRIIDeltacyt by MDA-MB-231 resulted in less bone destruction, less tumor with fewer associated osteoclasts, and prolonged survival compared with controls. Reversal of the dominant-negative signaling blockade by expression of a constitutively active TGF-beta type I receptor in the breast cancer cells increased tumor production of parathyroid hormone-related protein (PTHrP), enhanced osteolytic bone metastasis, and decreased survival. Transfection of MDA-MB-231 cells that expressed the dominant-negative TbetaRIIDeltacyt with the cDNA for PTHrP resulted in constitutive tumor PTHrP production and accelerated bone metastases. These data demonstrate an important role for TGF-beta in the development of breast cancer metastasis to bone, via the TGF-beta receptor-mediated signaling pathway in tumor cells, and suggest that the bone destruction is mediated by PTHrP.

Isolation and characterization of a cDNA clone encoding a novel peptide (OSF) that enhances osteoclast formation and bone resorption

Using an expression cloning approach, we identified and cloned a novel intracellular protein produced by osteoclasts that indirectly induces osteoclast formation and bone resorption, termed OSF. Conditioned media from 293 cells transiently transfected with the 0.9 kb OSF cDNA clone stimulated osteoclast-like cell formation in both human and murine marrow cultures in the presence or absence 10(-9) M 1,25-dihydroxyvitamin D3. In addition, conditioned media from 293 cells transfected with the OSF cDNA clone enhanced the stimulatory effects of 1,25-(OH)2D3 on bone resorption in the fetal rat long bone assay. In situ hybridization studies using antisense oligomers showed expression of OSF mRNA in highly purified osteoclast-like cells from human giant cell tumors of the bone. Northern blot analysis demonstrated ubiquitous expression of a 1.3 kb mRNA that encodes OSF in multiple human tissues. Sequence analysis showed the OSF cDNA encoded a 28 kD peptide that contains a c-Src homology 3 domain (SH3) and ankyrin repeats, suggesting that it was not a secreted protein, but that it was potentially involved in cell signaling. Consistent with these data, immunoblot analysis using rabbit antisera against recombinant OSF demonstrated OSF expression in cell lysates but not in the culture media. Furthermore, recombinant OSF had a high affinity for c-Src, an important regulator of osteoclast activity. Taken together, these data suggest that OSF is a novel intracellular protein that indirectly enhances osteoclast formation and osteoclastic bone resorption through the cellular signal transduction cascade, possibly through its interactions with c-Src or other Src-related proteins.

Immortalization of osteoclast precursors by targeting Bcl -XL and Simian virus 40 large T antigen to the osteoclast lineage in transgenic mice

Cellular and molecular characterization of osteoclasts (OCL) has been extremely difficult since OCL are rare cells, and are difficult to isolate in large numbers. We used the tartrate-resistant acid phosphatase promoter to target the bcl-XL and/or Simian Virus 40 large T antigen (Tag) genes to cells in the OCL lineage in transgenic mice as a means of immortalizing OCL precursors. Immunocytochemical studies confirmed that we had targeted Bcl-XL and/or Tag to OCL, and transformed and mitotic OCL were readily apparent in bones from both Tag and bcl-XL/Tag mice. OCL formation in primary bone marrow cultures from bcl-XL, Tag, or bcl-XL/Tag mice was twofold greater compared with that of nontransgenic littermates. Bone marrow cells from bcl-XL/Tag mice, but not from singly transgenic bcl-XL or Tag mice, have survived in continuous culture for more than a year. These cells form high numbers of bone-resorbing OCL when cultured using standard conditions for inducing OCL formation, with approximately 50% of the mononuclear cells incorporated into OCL. The OCL that form express calcitonin receptors and contract in response to calcitonin. Studies examining the proliferative capacity and the resistance of OCL precursors from these transgenic mice to apoptosis demonstrated that the increased numbers of OCL precursors in marrow from bcl-XL/Tag mice was due to their increased survival rather than an increased proliferative capacity compared with Tag, bcl-XL, or normal mice. Histomorphometric studies of bones from bcl-XL/Tag mice also confirmed that there were increased numbers of OCL precursors (TRAP + mononuclear cells) present in vivo. These data demonstrate that by targeting both bcl-XL and Tag to cells in the OCL lineage, we have immortalized OCL precursors that form bone-resorbing OCL with an efficiency that is 300-500 times greater than that of normal marrow.

Leukotriene B4 stimulates osteoclastic bone resorption both in vitro and in vivo

Upon activation, the enzyme 5-lipoxygenase converts arachidonic acid into principally three products, the peptidoleukotrienes, 5-hydroperoxyeicosatetraenoic acid (5-HETE) or the leukotriene B4. We have shown that the peptido-leukotrienes (known as LTC4, LTD4, or LTE4) and 5-HETE induce osteoclastic bone resorption and that receptors for LTD4 are present on isolated avian osteoclast-like cells. Here, we show the effects of the third metabolic product of the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism, the leukotriene LTB4, on osteoclastic bone resorption both in vivo and in vitro. Because LTB4 production is increased in a number of inflammatory conditions, it may be an important contributor to the bone loss which occurs in these disorders. LTB4 increased osteoclastic bone resorption in vivo following local administration over the calvariae of normal mice and in vitro in organ cultures of neonatal mouse calvariae. When LTB4 was injected over the calvaria of mice, there was a significant increase in bone resorption, osteoclast numbers, and eroded surfaces. LTB4 also increased the formation of resorption lacunae by isolated neonatal rat osteoclasts. Greater potency was observed with LTB4 compared with the peptido-leukotriene LTD4. This is in contrast to prostaglandins of the E series, which are reported to inhibit isolated osteoclasts. Experiments using marrow cultures suggest that LTB4 stimulates bone resorption in part by enhancing the formation of osteoclasts.

Evidence for a causal role of parathyroid hormone-related protein in the pathogenesis of human breast cancer-mediated osteolysis

Breast cancer almost invariably metastasizes to bone in patients with advanced disease and causes local osteolysis. Much of the morbidity of advanced breast cancer is a consequence of this process. Despite the importance of the problem, little is known of the pathophysiology of local osteolysis in the skeleton or its prevention and treatment. Observations in patients with bone metastases suggest that breast cancer cells in bone express parathyroid hormone-related protein (PTHrP) more frequently than in soft tissue sites of metastasis or in the primary tumor. Thus, the role of PTHrP in the causation of breast cancer metastases in bone was examined using human breast cancer cell lines. Four of eight established human breast cancer cell lines expressed PTHrP and one of these cell lines, MDA-MB-231, was studied in detail using an in vivo model of osteolytic metastases. Mice inoculated with MDA-MB-231 cells developed osteolytic bone metastasis without hypercalcemia or increased plasma PTHrP concentrations. PTHrP concentrations in bone marrow plasma from femurs affected with osteolytic lesions were increased 2.5-fold over corresponding plasma PTHrP concentrations. In a separate experiment, mice were treated with either a monoclonal antibody directed against PTHrP(1-34), control IgG, or nothing before tumor inoculation with MDA-MB-231 and twice per week for 26 d. Total area of osteolytic lesions was significantly lower in mice treated with PTHrP antibodies compared with mice receiving control IgG or no treatment. Histomorphometric analysis of bone revealed decreased osteoclast number per millimeter of tumor/bone interface and increased bone area, as well as decreased tumor area, in tumor-bearing animals treated with PTHrP antibodies compared with respective controls. These results indicate that tumor-produced PTHrP can cause local bone destruction in breast cancer metastatic to bone, even in the absence of hypercalcemia or increased circulating plasma concentrations of PTHrP. Thus, PTHrP may have an important pathogenetic role in the establishment of osteolytic bone lesions in breast cancer. Neutralizing antibodies to PTHrP may reduce the development of destructive bone lesions as well as the growth of tumor cells in bone.

Development and characterization of a human marrow stromal cell line that enhances osteoclast-like cell formation

We established a human bone marrow stromal cell line (Saka) by infecting marrow adherent cells from semisolid marrow cultures with a recombinant simian virus-40 (SV40) virus. The cells expressed SV40 large tumor antigen, had a fibroblast-like shape, and expressed fibronectin and vimentin. They did not contain detectable alkaline phosphatase activity; express myeloid, lymphoid, or factor VIII-associated antigens; or develop adipocyte-like characteristics with dexamethasone treatment. Polymerase chain reaction analysis of Saka cell RNA detected expression of messenger RNAs for interleukin-6 (IL-6), IL-1 beta, granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor, stem cell factor, and the 1,25-dihydroxyvitamin D3 receptor. Coculture of Saka cells with human marrow mononuclear cells enhanced formation of osteoclast-like multinucleated cells (MNC) in long term human bone marrow cultures. These MNC expressed calcitonin receptors and formed resorption lacunae on dentine. In contrast, coculture of marrow mononuclear cells with other SV40-transformed human marrow stromal cell lines did not increase MNC formation. Conditioned medium from Saka cells or coculture of bone marrow and Saka cells separated by a Millipore membrane did not enhance MNC formation. Addition of a neutralizing antibody to IL-6 or IL-1 beta blocked the effects of Saka cells on MNC formation. These results suggest that marrow stromal cells enhance osteoclast formation in part through direct cell to cell contact and production of IL-6 and/or IL-1 beta.

Use of an in vivo model to determine the effects of interleukin-1 on cells at different stages in the osteoclast lineage

In vitro model systems have been used extensively to study factors that affect osteoclast formation and to identify osteoclast precursors. However, in vitro systems do not examine the entire process of osteoclast differentiation simultaneously and lack accessory cells normally present in vivo. Additionally, the role that metabolism of the factor may play on its osteotropic activity in vivo is not addressed by these culture systems. Therefore, we have developed an in vivo model that permits us to examine simultaneously the effects of osteotropic factors on three distinct stages of osteoclast differentiation: (1) multipotent osteoclast precursors, the granulocyte-macrophage colony-forming unit (CFU-GM); (2) more differentiated marrow mononuclear osteoclast precursors; and (3) mature osteoclasts already present on bone surfaces. In the current study, we used interleukin-1 (IL-1) as a prototypic osteotropic factor to test the utility of this system to delineate the cellular mechanisms responsible for enhanced osteoclast activity stimulated by this cytokine. IL-1 induced hypercalcemia and enhanced the growth and differentiation of CFU-GM, increased the number of more committed mononuclear osteoclast precursors, and stimulated mature osteoclasts to resorb bone. These data demonstrate that this simple in vivo model permits the easy delineation of the stages of osteoclast development, in which osteotropic factors act to enhance bone turnover, and may be useful in understanding the mechanism of action of antiresorptive agents.

Interleukin-6 antisense deoxyoligonucleotides inhibit bone resorption by giant cells from human giant cell tumors of bone

The effects of antisense constructs to IL-6 on the bone-resorbing capacity of purified giant cells from giant cell tumors of bone were examined to further define the role of IL-6 in human osteoclastic bone resorption. In addition, we wanted to determine the utility of antisense constructs to cytokines produced by osteoclasts as probes to identify the molecular events responsible for the bone-resorptive process. Giant cells were cultured on sperm whale dentin for 24 h in the presence of fluoresceinated antisense or scrambled antisense deoxyoligonucleotides complementary to IL-6 mRNA. The giant cells actively incorporated these oligonucleotides, as evidenced by their intense fluorescence. The number of resorptive lacunae formed and the area of the dentin resorbed were significantly decreased in cultures of giant cells treated with antisense IL-6 constructs compared with control cultures treated with scrambled antisense constructs to IL-6 (60 +/- 13 versus 12 +/- 6 lacunae and 1.2 +/- 0.3 versus 0.26 +/- 0.1 x 10(5) microns2). IL-6 levels in conditioned media from giant cell cultures treated with IL-6 antisense constructs were fourfold lower than those in control media obtained from giant cells treated with scrambled antisense constructs to IL-6. These data confirm the capacity of IL-6 antisense oligomers to block IL-6 production by these cells. These observations show that IL-6 plays an important role in the bone-resorptive process of human osteoclasts and suggest that antisense constructs to cytokines produced by bone cells may be useful for determining the molecular events occurring during bone resorption.

On the relationship between autobiographical memory and perceptual learning

Although the majority of research on human memory has concentrated on a person's ability to recall or recognize items as having been presented in a particular situation, the effects of memory are also revealed in a person's performance of a perceptual task. Prior experience with material can make that material more easily identified or comprehended in perceptually difficult situations. Unlike with standard retention tests, effects of prior experience on a perceptual task do not logically require that a person be aware that he or she is remembering. Indeed, amnesic patients purportedly show effects of practice in their subsequent performance of a perceptual or motor task even though they profess that they do not remember having engaged in that prior experience. The experiments that are reported were designed to explore the relationship between the more aware autobiographical form of memory that is measured by a recognition memory test and the less aware form of memory that is expressed in perceptual learning. Comparisons of effects on perceptual learning and recognition memory reveal two classes of variables. Variables such as the level of processing of words during study influenced recognition memory, although they had no effect on subsequent perceptual recognition. A study presentation of a word had as large an effect on its later perceptual recognition when recognition memory performance was very poor as it did when recognition memory performance was near perfect. In contrast, variables such as the number and the spacing of repetitions produced parallel effects on perceptual recognition and recognition memory. Following Mandler and others, it is suggested that there are two bases for recognition memory. If an item is readily perceived so that it seems to "jump out" from the page, a person is likely to judge that he or she has previously seen the item in the experimental situation. Variables that influence ease of perceptual recognition, then, can also have an effect on recognition memory, so parallel effects are found. The second basis for recognition memory involves elaboration of a word's study context and depends on such factors as level of processing during study--factors that are not important for perceptual recognition of isolated words. Comparisons of perceptual recognition and recognition memory are shown to be useful for determining how a variable has its effect. Effects of study on perceptual recognition appear to be totally due to memory for physical or graphemic information. Results reported are also relevant to theories of perceptual learning. A single presentation of an item is shown to have large and long-lasting effects on its later perceptual recognition. At least partially, effects of study on perceptual recognition depend on the same variables as do effects on more standard memory tests.

On the relationship between autobiographical memory and perceptual learning

Although the majority of research on human memory has concentrated on a person's ability to recall or recognize items as having been presented in a particular situation, the effects of memory are also revealed in a person's performance of a perceptual task. Prior experience with material can make that material more easily identified or comprehended in perceptually difficult situations. Unlike with standard retention tests, effects of prior experience on a perceptual task do not logically require that a person be aware that he or she is remembering. Indeed, amnesic patients purportedly show effects of practice in their subsequent performance of a perceptual or motor task even though they profess that they do not remember having engaged in that prior experience. The experiments that are reported were designed to explore the relationship between the more aware autobiographical form of memory that is measured by a recognition memory test and the less aware form of memory that is expressed in perceptual learning. Comparisons of effects on perceptual learning and recognition memory reveal two classes of variables. Variables such as the level of processing of words during study influenced recognition memory, although they had no effect on subsequent perceptual recognition. A study presentation of a word had as large an effect on its later perceptual recognition when recognition memory performance was very poor as it did when recognition memory performance was near perfect. In contrast, variables such as the number and the spacing of repetitions produced parallel effects on perceptual recognition and recognition memory. Following Mandler and others, it is suggested that there are two bases for recognition memory. If an item is readily perceived so that it seems to "jump out" from the page, a person is likely to judge that he or she has previously seen the item in the experimental situation. Variables that influence ease of perceptual recognition, then, can also have an effect on recognition memory, so parallel effects are found. The second basis for recognition memory involves elaboration of a word's study context and depends on such factors as level of processing during study--factors that are not important for perceptual recognition of isolated words. Comparisons of perceptual recognition and recognition memory are shown to be useful for determining how a variable has its effect. Effects of study on perceptual recognition appear to be totally due to memory for physical or graphemic information. Results reported are also relevant to theories of perceptual learning. A single presentation of an item is shown to have large and long-lasting effects on its later perceptual recognition. At least partially, effects of study on perceptual recognition depend on the same variables as do effects on more standard memory tests.