Main Street Bank lends most of its money to small businesses and is earning decent profits. But the Kingwood, Texas, bank is about to get out of the banking business. In an extreme example of the frustration felt by many bankers as regulators toughen their oversight of the nation's financial institutions, Main Street's chairman, Thomas Depping, is expected to announce Wednesday that the 27-year-old bank will surrender its banking charter and sell its four branches to a nearby bank. Mr. Depping plans to set up a new lender that will operate beyond the reach of banking regulators—and the deposit-insurance safety...