Prolactin influences proliferation and apoptosis of a human IgE secreting myeloma cell line, U266.

In certain types of solid tumours and lymphomas prolactin (PRL) potentiates tumour cell proliferation and exerts anti-apoptotic effect. Tumour cells themselves can produce PRL and express PRL-receptors. Hyperprolactinemia is associated with different tumours, also. Multiple myeloma (MM) is a haematological malignancy caused by the clonal expansion of terminally differentiated plasma cells in the bone marrow. Recently, we demonstrated PRL immunostaining in bone marrow cells of MM patients and an elevated level of serum PRL of MM patients with advanced disease. In the present study, we tested the effect of PRL on a U266 human myeloma cell line and demonstrated constitutive and melphalan-stimulated intracytoplasmic PRL in U266 cells. Exogeneous PRL inhibited the proliferation and immunoglobulin (Ig) production of U266 myeloma cells. Concerning etoposide-induced apoptosis, PRL had a double-faceted effect depending on the applied dose: high, pharmacological doses (corresponding to hyperprolactinemia), inhibited apoptosis, whereas near physiological doses exerted a pro-apoptotic effect. These data indicate a definite effect of PRL on a human myeloma cell line. We demonstrated a direct inhibition of PRL on tumour cell growth, while its reciprocal effect on apoptosis refers to an important regulatory role of PRL.