Human papillomavirus (HPV) testing in the management of women with abnormal Pap smears. Experience of a colposcopy referral clinic

BACKGROUND AND OBJECTIVES

Several detailed algorithms for the appropriate use of human papillomavirus (HPV) testing in the management of women with abnormal Pap (Papanicolaou) smears have been launched, but their direct country-to-country adoption is difficult. This necessitates their testing in individual settings, which is ongoing in our colposcopy referral clinic.

METHODS

A series of 224 consecutive women attending the clinic with the usual referral indications (ASC-US or higher in Pap) were examined by the conventional diagnostic tools (PAP smear, colposcopy, punch biopsy) and subjected to HPV testing and viral typing for both low-risk (L-R) and high-risk (H-R) types by nested PCR-based techniques. Predictors of the high-grade diagnostic categories were analysed using both univariate- and multivariate modelling, and the performance characteristics (sensitivity, specificity, NPV, PPV) of all tests in detecting high-grade CIN were calculated.

RESULTS

In the PAP test, ASC-US smears were most common (37.9%), followed by low-grade squamous intraepithelial lesions (LSIL) (26.3%) and high-grade SIL (HSIL) (4.9%). Colposcopy was performed for 180 women, of whom 48.3% had a normal transformation zone (TZ), 40.6% had ATZ1 (abnormal TZ grade 1), and 5.6% had ATZ2. In biopsy (n = 71), 49.3% had CIN1, 5.6% CIN2, and 16.9% CIN3. The HPV test was positive in 64 (28.8%) women, more often in those aged < 35 years (p = 0.025). High-grade colposcopy (ATZ2) was significantly associated with HSIL in the Pap test (OR 20.5; 95% CI: 4.34-96.47), and with HPV test positivity (OR 6.37; 95% CI: 1.58-25.73). The most significant predictors of CIN3 were HSIL in the PAP, HPV test positivity, and high-grade colposcopy. HSIL and HPV test (for H-R types), but not colposcopy, retained their significance as independent predictors of CIN3 also in adjusted multivariate models: OR 88.27; 95% CI 4.17-1867.04, and OR 19.46; 95% CI 2.01-187.75, for the HSIL and H-R HPV test, respectively. Changing the cut-off level of the Pap test from ASC-US to HSIL increased the specificity of the test up to 96.4%, with the loss in sensitivity from 87.5% to 43.8%. Colposcopy (ATZ2) had 92% specificity, and NPV competing with that of the Pap test. The sensitivity of HPV test exceeds that of the Pap test at HSIL cut-off level, but the specificity of the PAP test is clearly superior.

CONCLUSIONS

Accurate predictors of significant cervical pathology (CIN3) are well defined, but the problem is the different performance of the diagnostic tools in clinical practice. A proficient combination of the tests is likely to result in the most satisfactory clinical practice in the management of women with abnormal Pap tests (MAPS).

Macrophage migration inhibitory factor in human pregnancy and labor

PROBLEM

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine involved in reproduction. Presently there is no information on the possible involvement of MIF in the onset of labor.

METHODS

Macrophage migration inhibitory factor was assayed, by enzyme-linked immunosorbent assay (ELISA), in maternal serum (MS) and amniotic fluid (AF) both, at midtrimester and at term, as well as in cord serum (CS) at birth. Extraembryonic membranes were analyzed by immunohistochemistry.

RESULTS

Amniotic fluid MIF concentrations were significantly higher at term (median 62.10 ng/mL) than at midtrimester (median 20.07 ng/mL) and reached a peak in term labor (median 258.80 ng/mL). The AF/MS ratio varied from a median of 4.34 at midtrimester and 33.7 at term labor. The MS/CS ratio was 0.4. Migration inhibitory factor immunoreactivity was found in different cell layers of the extraembryonic membranes.

CONCLUSIONS

The increased secretion of MIF in AF at term, particularly at term labor, suggests that MIF contributes to the inflammatory events leading to labor.

Hormonal regulation of cytokine release by human fetal membranes at term gestation: effects of oxytocin, hydrocortisone and progesterone on tumour necrosis factor-alpha and transforming growth factor-beta 1 output

Inflammatory cytokines can play an important role in the biomolecular processes leading to labour by regulating prostaglandin production in intrauterine tissues. In the setting of intrauterine infection, an increased production of these cytokines by placenta, decidua and fetal membranes occurs and is responsible for the onset and maintenance of preterm labour. However, the factors involved in the control of cytokine release by these tissues in normal pregnancy at term are still largely unknown. We investigated the possibility that the synthesis and release of tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) by human fetal membranes at term gestation is regulated by several hormones potentially involved either in the maintenance of pregnancy or in the parturitional process. In the present study, the effects of hydrocortisone, progesterone and oxytocin on TNF-alpha and TGF-beta1 release by explants of fetal membranes at term gestation were evaluated. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to assess the effect of the above hormones on mRNA expression; TNF-alpha and TGF-beta1 release in culture medium was quantitifed by ELISA assays. Results show that both tissue mRNA expression for TNF-alpha and TNF-alpha release in culture medium were significantly increased by oxytocin, but not by hydrocortisone and progesterone. On the contrary, all the hormones tested increased both tissue TGF-beta1 mRNA expression and release in culture medium. These findings suggest that TNF-alpha and TGF-beta1 production by human fetal membranes in uncomplicated pregnancy at term is selectively modulated by oxytocin, hydrocortisone and progesterone.

Simultaneous vulvar intraepithelial neoplasia and Paget's disease: report of two cases

We describe a very rare association between intraepithelial, extramammary Paget's disease and human papillomavirus- (HPV) negative, keratinized type of VIN III observed in two elderly women. In both cases, morphological and immunohistochemical investigation showed two heterogeneous but intimately admixed neoplastic populations of vulvar epithelium. Atypical keratinocytes stained markedly and diffusely positive for high molecular weight cytokeratins, and moderately for p53 protein and c-erbB-2 immunostainings. Paget cells were diffusely positive for CEA, EMA, and low molecular weight cytokeratins, moderately and focally for c-erbB-2 and (in one case) for S-100. Morphological and immunohistochemical phenotypic differences between Paget cells and atypical keratinocytes suggest a simultaneous and incidental association of two distinct neoplastic disorders more than a mixed carcinoma in situ of vulvar epithelium.

[Embolization of the uterine artery in the treatment of uterine myoma]

PURPOSE

To propose uterine myoma embolization as an alternative to myomectomy or hysterectomy in the treatment of symptomatic myomas; to evaluate the efficacy of the procedure in terms of clinical outcome, adopting all procedural and technical precautions to ensure minimal X-ray exposure and preserve reproductive potential.

MATERIAL AND METHODS

Between April 1998 and February 2000, 26 patients, age range 32-54 years (mean 41 years), underwent uterine arterial embolization for menorrhagia, pelvic pain, and sensation of mass and pressure. Inclusion criteria were: single myomas, intramural localization and rich vascolarization of the lesion. Dose to patient was obtained by placing a thermoluminescent dosimeter (Harshaw, Solon, Ohio) both placed in posterior fornix of the vagina and on the skin at the beam entrance site. The procedure was performed under peridural anesthesia; polyvinil alcohol particles 355-500 mu (Contour) (Target Therapeutics, Boston Scientific Corporation, Fremont CA, USA) were employed as embolic agent. The uterine arteries were incannulated with a 5F (Glidecath, Terumo, Europe NV, Belgium) and successively 3F coaxial microcatheter (Target, Boston Scientific Corporation, Fremont CA, USA); the embolic material was injected as distally as possible. Color Power Doppler Ultrasound follow-up before and after i.v. contrast media administration (Levovist SHU 508 A, Shering, Berlin, Germany) was carried out at 15 days, at 1, at 3, at 6 months, and at 1 year from embolization. Pre-procedural evaluation and follow-up at 1 year was performed by MRI using T1 and T2 weighted images before and after Gadolinium (GdDTPA Shering, Berlin, Germany) administration.

RESULTS

The technical success of the interventional procedure was 100% (26/26 cases). The mean fluoroscopy time was 20 minutes, and the mean number of angiographic exposures was 10. The mean estimated ovarian dose was 18.75 cGy and the mean adsorbed skin dose was 126.71 cGy. The imaging follow-up showed a 55% reduction of myoma volume at 6 months and a 75% reduction at 1 year. All patients reported a marked decrease in symptoms. No major complications were observed. The appearance of pelvic pain in the 24-48 hours after the procedure required sedation by analgesic pump; transitorial amenorrhea was observed in 3 patients. As for term complications, 2 patients have eliminated necrotic material through the vagina four weeks after procedure. The patients reported great satisfaction with the procedure.

DISCUSSION

Many treatment options are currently available for symptomatic uterine myomas. One is surgical myomectomy which is associated with increased blood loss, pain and post operative morbidity and requires an additional surgical procedure for fibroma recurrence in 20-25% of patients. Another alternative treatment is hormonal therapy, which drammatically improves symptoms and reduces fibroid size although leiomyomas regrow to their original size within a few months of discontinuing treatment. Uterine embolization is a relatively new treatment for uterine fibroids that can be considered as an alternative to surgical and medical procedures. The radiation exposure adsorbed by the patient is reduced by using pulsed fluoroscopy and taking all the precautionary measures required to minimize the dose.

CONCLUSIONS

The technical success, the patient' satisfation, the short hospitalization time and preservation of fertility confer to uterine artery embolization the role of a new alternative therapy for the treatment of symptomatic uterine myomas.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP-receptor type 1 expression in rat and human placenta

Pituitary adenylate cyclase-activating polypeptide (PACAP), the new hypophysiotropic factor member of the vasoactive intestinal peptide (VIP)/secretin/glucagon/GHRH family of neuropeptides, exerts its biological action by interacting with both PACAP-selective type I receptors (PAC1) and type II receptors (VPAC1), which bind both PACAP and VIP. The placenta is a site of production of hypophysiotropic factors that participate in the control of local hormone production, as well as the respective hypothalamic-pituitary neurohormones. In the present study, we show the expression of PACAP gene and irPACAP distribution within rat and human placental tissues, by means of RT-PCR and immunohystochemical experiments. In both rat and human placenta, we evaluated the expression of PAC1 gene by Northern hybridization analysis performed with a 32P-labeled 706 nt complementary DNA probe, derived from the full-length coding region of the rPAC1 complementary DNA. The results of these experiments demonstrate the presence, in both human and rat placenta, of a 7.5-kb transcript similar in size to those detected in the ovary, brain, and hypothalamus. Alternative splicing of two exons occurs in human and rat PAC1 gene generating splice variants with variable tissue-specific expression. To ascertain which of the splice variants were expressed in placental tissue we performed RT-nested PCR using primers flanking the insertion sequence termed hip/hop cassette in rat or SV1/SV2 box in human gene. Electrophoretic analysis of the PCR products showed a different pattern of expression of messenger RNA splicing variants in human and rat placenta. In particular, the rat placenta expresses the short PAC1 receptor (PAC1short), the rPAC1-hip or hop (which are indistinguishable with the primers used), and the rPAC1-hip-hop, whereas the human placenta expresses only the PAC1SV1 (or SV2) variant, structurally homologous to the rat PAC1 hip (or hop). Sequence analysis of the human PCR-amplified PAC1 variant was therefore carried out and revealed that human placenta only expresses the PAC1SV2 isoform. The presence and characterization of PACAP binding sites was then investigated in human placenta by radioligand binding studies performed on crude membrane preparation using [125I]PACAP27 as tracer. Scatchard analysis of the binding results revealed the presence of two binding sites, one with high affinity and low capacity (Kd 0.33+/-0.04 nM; Bmax 36.9+/-12.1 fmol/mg protein) and one with low affinity and high capacity (Kd 24+/-6.9 nM, Bmax 9.3+/-0.19 pmol/mg protein). The relative potencies of PACAP-related peptides for inhibition ofradioligand binding were: PACAP27 > or = PACAP38 > VIP, whereas GHRH and other unrelated peptides, such as CRH and beta-endorphin, did not inhibit [125I]PACAP27 binding. In conclusion, in this study, we provide evidence for the expression of PACAP within rat and human placenta. We also demonstrate that both human and rat placenta express the PAC1 gene and that the human tissue has binding sites for PACAP. These findings may suggest a role for PACAP in the regulation of placental physiology through autocrine and/or paracrine mechanisms.

Urocortin stimulates placental adrenocorticotropin and prostaglandin release and myometrial contractility in vitro

Urocortin is a new member of the CRF family. Multiple biological effects for urocortin have been shown in rats and in some in vitro models, showing a modulatory role in hormonal and behavioral functions. Human placenta expresses urocortin, but no information is available on the possible local biological actions. The aim of the present study was to evaluate the effect of urocortin on placental ACTH and prostaglandin (PG) secretion, as well as on myometrial contractility. Various in vitro models were used. For investigating the effect of urocortin on ACTH release, primary cultures of human trophoblast cells were used. Culture media, collected before and after 3 h exposure to different doses of urocortin and ACTH, were measured by RIA. Trophoblast tissue explants were incubated for 24 h in the presence of increasing doses of urocortin, and prostaglandin E2 (PGE2) levels were measured by RIA. Strips of myometrial tissue were incubated in an organ bath and connected to an isometric smooth-muscle transducer in the presence of urocortin, with or without prostaglandin F2alpha (PGF2a). In all these experiments, the effect of astressin (a CRF receptor antagonist) on urocortin-induced actions and the effect of equimolar doses of CRF were evaluated. A dose-related increase of trophoblast ACTH or PGE2 was induced by urocortin, whereas astressin inhibited urocortin-stimulated ACTH or PGE2 release. Equimolar doses of CRF showed a similar effect on both ACTH and PGE2. Urocortin increased PGF2alpha-induced myometrial contractility, and this effect was completely abolished by the addition of astressin. The present study showed that human urocortin stimulates placental secretion of ACTH and PGE2, and modulates myometrial contractility, suggesting a role for this peptide in placental and intrauterine CRF pathways.

Interrelationships between oxytocin and eicosanoids in human fetal membranes at term gestation: which role for leukotriene B4?

The existence of a functional paracrine loop between oxytocin and prostaglandin F2-alpha in human placental cells has been demonstrated. The present study was undertaken to investigate further the possible interrelationships between oxytocin and eicosanoids in human intrauterine tissues at term gestation. Therefore, we evaluated the effect of leukotriene B4 (LTB4) on oxytocin (OT) production by explants of fetal membranes and amnion and the effect of oxytocin on the production of LTB4 and prostaglandin E2 (PGE2) by both fetal membranes and amnion. In all cases studied (n = 25), short-term cultures of tissue explants (fetal membranes or amnion) have been carried out. The production of eicosanoids and oxytocin in culture medium was evaluated. Oxytocin measurement was carried out by radioimmunoassay following extraction of the substance with Sep Pak C18 cartridges, PGE2 and LTB4 were measured by radioimmunoassay directly in culture medium. Results show that LTB4 has no significant stimulatory effect on oxytocin production by fetal membranes or amnion tissue. On the other hand, oxytocin stimulates PGE2 release by both fetal membranes and isolated amnion, but has no effect on LTB4 production by these tissues. Taken together, these findings suggest the following conclusions: (1) a paracrine loop between LTB4 and oxytocin is lacking in fetal membranes and amnion at term pregnancy; (2) oxytocin exerts a stimulatory effect on PGE2 release by both fetal membranes and amnion; (3) the interrelationships between oxytocin and the different eicosanoids in the above tissues seem to be highly selective.

Effects of glucocorticoids and progesterone on prostaglandin E2 and leukotriene B4 release by human fetal membranes at term gestation

The present study was undertaken to evaluate the effects of the glucocorticoid hormones betamethasone and hydrocortisone, and of progesterone on the relative production of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) by explants of human fetal membranes at term gestation in the absence of labor. Tissues (n = 7) were incubated either in the presence or in the absence of the above mentioned hormones. PGE2 and LTB4 were measured in culture medium by radioimmunoassays. Glucocorticoids and progesterone did not affect PGE2 output by tissues; however, they greatly stimulated LTB4 production. Moreover, both betamethasone and hydrocortisone significantly increased the ratio of LTB4 to PGE2 formation by tissues. These results suggest that glucocorticoid hormones and progesterone might influence arachidonic acid metabolism in human fetal membranes by stimulating the production of lipoxygenase rather than cyclooxygenase substances before the onset of labor.

Nitric oxide in human fetal membranes at term gestation: effect on prostaglandin E2 release

OBJECTIVES

To examine the in vitro release of nitric oxide (NO) by human fetal membranes at term gestation and to investigate whether NO could stimulate prostaglandin E2 (PGE2) release by these tissues.

STUDY DESIGN

Explants of fetal membranes (n = 17) were incubated either in the presence of sodium nitroprusside (NP), or L-Arginine (L-Arg), or bacterial lipopolysaccharide (LPS), or in the absence of the above substances (controls). NO and PGE2 concentrations in culture medium were assayed by the Griess reaction and radioimmunoassay, respectively.

RESULTS

Fetal membranes spontaneously released NO in culture medium; incubation with NP increased the production of both NO and PGE2. L-Arg and LPS enhanced PGE2 output by tissues but did not influence NO production.

CONCLUSIONS

An NO-generating activity might be present in human fetal membranes. NO stimulates PGE2 release by these tissues.

Release of arachidonic acid metabolites by human fetal membranes: interrelationship between leukotriene B4 and prostaglandin E2

The objective of this study was to ascertain whether human fetal membranes metabolize arachidonic acid preferentially through the lipoxygenase rather than the cyclooxygenase pathway before labor and whether an interaction between lipoxygenase and cyclooxygenase products is present in these tissues. Reflected fetal membranes were obtained from 8 healthy women at term gestation who were delivered by elective repeat cesarean section before the onset of labor. Tissues were cultured either in the presence or in the absence of the calcium ionophore A23187 for 60 minutes. Leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) were measured in culture medium by radioimmunoassays. Moreover, the effect of different concentrations of exogenously added LTB4 on PGE2 release was evaluated. The basal and stimulated output of LTB4 by tissues was significantly higher than that of PGE2. Addition of LTB4 significantly decreased PGE2 release by tissues. These findings suggest that in the above tissues: 1) the arachidonate lipoxygenase pathway is highly active before labor; 2) LTB4 might play a role in the regulation of PGE2 production.

Obstetric and perinatal outcome in human immunodeficiency virus-infected pregnant women with and without opiate addiction

This study was undertaken to assess the impact on gestation played by the simple human immunodeficiency virus (HIV)-seropositive status either alone or complicated by opiate abuse in the absence of other confounding variables. To this purpose the main obstetric complications and the perinatal outcome were prospectively evaluated in 38 simple HIV-infected women, 14 of whom were simple carriers and 24 under methadone treatment, and in 76 uninfected women, 16 of whom were methadone users and 60 controls. In simple HIV-carriers maternal weight gain (P < 0.001) and both 1- and 5-min Apgar scores (P < 0.005) were reduced whereas the incidence of miscarriage was increased (P < 0.05). Worse obstetric and perinatal outcomes were found in HIV-seropositive drug addicts, in which gestational length (P < 0.001), maternal weight gain (P < 0.001) and Apgar scores were lower (P < 0.005 and P < 0.001, respectively) and the rate of preterm labour, small for gestational age newborns, vaginal and urinary infections as well as of unexplained fever (P < 0.05) was higher. Outcomes were similar in HIV-seropositive and seronegative drug addicts and in both groups a positive correlation (r = 0.62 P < 0.001, and r = 0.44, respectively) was found between the number of infectious episodes throughout pregnancy and the mean dose of opiate consumed daily. Our results suggest that HIV-seropositive condition might exert slight direct and indirect detrimental effects on pregnancy. Whatever the maternal serologic status, opiate intake not only causes a further worsening of gestational and perinatal outcomes, but also increases the susceptibility towards pathogens.

Oxytocin in human intrauterine tissues at parturition

The recent detection of oxytocin (OT) mRNA in human gestational tissues suggests that OT may be locally synthesized and released to act on the uterus as a local mediator in the mechanism of parturition. In order to investigate this possibility the OT immunoreactive (I.R.) content was examined directly in placental decidua and amniochorial membranes after term and preterm delivery and in their culture media at term gestation. I.R.OT concentrations were also measured in maternal, retroplacental and umbilical plasma as well as in amniotic fluid in the presence or the absence of labour. Low I.R.OT concentrations (below 15 fmol g-1 wet tissue) were found in both amniochorial membranes and placental decidua. Moreover, whereas in amniochorion they were higher (P < 0.05) after preterm than term spontaneous parturition, in decidua they were higher (P < 0.05) after term than preterm vaginal delivery. Detectable amounts (below 15 fmol g-1 wet tissue per h) of I.R.OT were also found in culture media from explants of the above tissues. Among all the examined maternal and fetal fluids a rise in I.R.OT content at parturition was detected only in the amniotic liquor (P < 0.05). These findings suggest that I.R.OT concentrations in intrauterine tissues are very low; however, considering that OT is the most potent endogenous uterotonic agent, OT as such concentrations might play a paracrine function in the biochemical events leading to human parturition. Therefore, a role for amniotic OT in parturition can not be excluded.

Efficacy of CO2 laser surgery in treating squamous intraepithelial lesions. An analysis of clinical and virologic results

This paper reports the clinical and virologic results of CO2 laser treatment for squamous intraepithelial lesions in 154 patients. On the basis of cervical canal involvement, vaporization or conization was performed. Failure rates following the first and second treatments were 4.5% and 0%, respectively. However, human papillomavirus persistence in several women with completely normal follow-up suggests that one of the possible mechanisms of failure could be reexposure of the healing area to a viral reservoir within the "normal" epithelium.

SH-PTP2/Syp SH2 domain binding specificity is defined by direct interactions with platelet-derived growth factor beta-receptor, epidermal growth factor receptor, and insulin receptor substrate-1-derived phosphopeptides

Signaling by tyrosine kinases involves direct associations between proteins with Src homology 2 (SH2) domains and sites of tyrosine phosphorylation. Specificity in signaling pathways results in part from inherent selectivity in interactions between particular SH2 domains and phosphopeptide sequences. The cytoplasmic phosphotyrosine phosphatase SH-PTP2 (Syp, PTP 1D, PTP-2C) contains two SH2 domains (N and C) which mediate its association with and activation by the platelet-derived growth factor (PDGF) and epidermal growth factor receptors and IRS-1. We have developed a competitive phosphopeptide binding assay to analyze specificity of the SH-PTP2 N-SH2 domain for phosphorylation sites of these phosphoproteins. The sequence surrounding Tyr1009 bound with greatest affinity (ID50 = 14 microM) of eight PDGF receptor-derived phosphopeptides tested. No peptides corresponding to known epidermal growth factor receptor phosphorylation sites bound with high affinity. However, an alternative sequence surrounding Tyr954 bound tightly (ID50 = 21 microM). Of the 13 IRS-1-related peptides analyzed, sequences surrounding Tyr546, Tyr895, and Tyr1172 bound with highest affinity (ID50 = 11, 4, and 1 microM, respectively). Alternative phosphopeptides generally bound with much weaker affinity (ID50 > 150 microM). These findings are consistent with recent mutational analyses of the PDGF receptor and predict site-specific interactions between SH-PTP2 and each of these phosphoproteins. Comparisons between peptide sequences suggest that the N-terminal SH2 domain of SH-PTP2 binds with highest affinity to phosphotyrosine (pY) followed by a beta-branched residue (Val, Ile, Thr) at pY+1 and a hydrophobic residue (Val, Leu, Ile) at pY+3 positions. Peptide truncation studies also indicate that residues outside of the pY-1 to pY+4 motif are required for high affinity interactions.

Interleukin-3 stimulates prostaglandin E2 release by human fetal membranes at term gestation

The effect of interleukin-3 (IL-3) on prostaglandin E2 (PGE2) release by human fetal membranes at term gestation was evaluated. It was found that interleukin-3 stimulates in vitro prostaglandin E2 release by these gestational tissues, suggesting that interleukin-3 might be involved in the regulation of arachidonic acid metabolism in the fetal membranes.

Phosphatidylinositol 3-kinase p85 SH2 domain specificity defined by direct phosphopeptide/SH2 domain binding

We have developed a competition binding assay to quantify relative affinities of isolated Src-homology 2 (SH2) domains for phosphopeptide sequences. Eleven synthetic 11-12-amino acid phosphopeptides containing YMXM or YVXM recognition motifs bound to a PI 3-kinase p85 SH2 domain with highest affinities, including sequences surrounding phosphorylated tyrosines of the PDGF, CSF-1/c-Fms, and kit-encoded receptors, IRS-1, and polyoma middle T antigens; matched, unphosphorylated sequences did not bind. A scrambled YMXM phosphopeptide or sequences corresponding to the GAP or PLC-gamma SH2 domain binding motifs of the PDGF, FGF, and EGF receptors bound to the p85 SH2 domain with 30-100-fold reduced affinity, indicating that this affinity range confers specificity. Binding specificity was appropriately reversed with an SH2 domain from PLC-gamma: a phosphopeptide corresponding to the site surrounding PDGF receptor Tyr1021 binds with approximately 40-fold higher affinity than a YMXM-phosphopeptide. We conclude that essential features of specific phosphoprotein/SH2 domain interactions can be reconstituted using truncated versions of both the phosphoprotein (a phosphopeptide) and cognate SH2 domain-containing protein (the SH2 domain). SH2 domain binding specificity results from differences in affinity conferred by the linear sequence surrounding phosphotyrosine.